Seasonal Hydrography of Ameralik: A Southwest Greenland Fjord Impacted by a Land‐Terminating Glacier

Abstract

Greenland's coastal zone encompasses a large number of fjords, many of which are impacted by glacial meltwater runoff from land‐terminating glaciers. This type of fjord has received limited research attention, yet may represent the future of other fjords currently impacted by marine‐terminating glaciers that are retreating. In this study we describe the seasonal hydrography of Ameralik, a fjord on the southwest coast of Greenland impacted by a land‐terminating glacier. To complement this analysis we compare our results with observations from the neighbouring Godthåbsfjord, which receives meltwater from both land‐ and marine‐terminating glaciers. We find that the absence of subglacial discharge and glacial ice in Ameralik has a strong impact on the inner fjord density profiles and on circulation. The mean temperature of the upper 50 m layer was lower in Ameralik than Godthåbsfjord in May, but by September was 2°C higher in Ameralik. Dense coastal inflows occur in the late winter months in Ameralik, flushing the fjord and contributing to the return to a weakly stratified state. During the runoff period the surface waters are subject to estuarine circulation and wind forcing, while at intermediate depths a density gradient between the inner and outer fjord regions produces an intermediate baroclinic circulation, resulting in the exchange of water in this layer and the deepening of isopycnals. During summer a large fraction of the meltwater runoff is retained within the fjord rather than being exported. A substantial export of this summer accumulated freshwater occurs in connection with coastal inflows during winter.

Full text

1. Introduction
As a consequence of rapid climate change in the Arctic region, the Greenland Ice Sheet (GrIS) has suffered
substantial mass loss in recent decades (Shepherd etal.,2020; Simonsen etal.,2021; Smith etal.,2020). For the
surrounding fjord systems this translates to large scale glacial retreat with increased freshwater fluxes into fjords
(e.g., King etal.,2020; Rignot etal.,2016). Changes in fjord hydrography subsequently affect the range of roles
performed by these systems that act as transition zones between the GrIS and the open ocean. They support com-
plex and productive ecosystems (Arendt etal.,2016; Meire etal.,2017), play a key role in regulating heat trans-
port to glaciers, and transform and export freshwater from the GrIS to the continental shelf (Beaird etal.,2018;
Mortensen etal.,2018; Straneo & Cenedese,2015).
A major challenge in predicting the response of fjords to glacial retreat, as well as other consequences of climate
change, lies in the inherent diversity of these systems. Hydrography in fjords is not easily generalized, owing in
part to the contributions of regional differences (e.g., ocean water masses, local climate) and variation in physical
Abstract Greenland's coastal zone encompasses a large number of fjords, many of which are impacted
by glacial meltwater runoff from land-terminating glaciers. This type of fjord has received limited research
attention, yet may represent the future of other fjords currently impacted by marine-terminating glaciers that
are retreating. In this study we describe the seasonal hydrography of Ameralik, a fjord on the southwest coast
of Greenland impacted by a land-terminating glacier. To complement this analysis we compare our results with
observations from the neighbouring Godthåbsfjord, which receives meltwater from both land- and marine-
terminating glaciers. We find that the absence of subglacial discharge and glacial ice in Ameralik has a strong
impact on the inner fjord density profiles and on circulation. The mean temperature of the upper 50m layer was
lower in Ameralik than Godthåbsfjord in May, but by September was 2°C higher in Ameralik. Dense coastal
inflows occur in the late winter months in Ameralik, flushing the fjord and contributing to the return to a
weakly stratified state. During the runoff period the surface waters are subject to estuarine circulation and wind
forcing, while at intermediate depths a density gradient between the inner and outer fjord regions produces
an intermediate baroclinic circulation, resulting in the exchange of water in this layer and the deepening of
isopycnals. During summer a large fraction of the meltwater runoff is retained within the fjord rather than
being exported. A substantial export of this summer accumulated freshwater occurs in connection with coastal
inflows during winter.
Plain Language Summary Marine-terminating glaciers around Greenland are retreating, impacting
the adjacent fjords with potential changes in the pathways taken by glacial meltwater. Few studies focus on
fjords that receive meltwater only from land-terminating glaciers, although knowledge of these systems can
help us better understand how water from melting glaciers eventually ends up in the ocean in a future warmer
climate. Here we present a full year of temperature and salinity observations from one such fjord on the
southwest coast of Greenland and use these measurements to describe seasonal changes in water properties
and circulation patterns. We compare the results with observations from a neighbouring fjord which receives
meltwater from both land- and marine-terminating glaciers. This comparison allows us to link differences
observed between the fjords with the water movements associated with the type of glacier. While physical
properties of the fjords, such as sill depth, play an important role in the circulation, the meltwater pathway also
influences fjord hydrography, most prominently in the surface layers. This study will help us to understand the
potential future state for many Greenland fjords with glaciers that are presently marine-terminating.
STUART-LEE ET AL.
© 2021. The Authors.
This is an open access article under
the terms of the Creative Commons
Attribution License, which permits use,
distribution and reproduction in any
medium, provided the original work is
properly cited.
Seasonal Hydrography of Ameralik: A Southwest Greenland
Fjord Impacted by a Land-Terminating Glacier
A. E. Stuart-Lee1 , J. Mortensen2 , A.-S. van der Kaaden1, and L. Meire1,2
1Department of Estuarine and Delta Systems, Royal Netherlands Institute for Sea Research, Yerseke, The Netherlands,
2Greenland Climate Research Centre, Greenland Institute of Natural Resources, Nuuk, Greenland
Key Points:
• We present seasonal hydrography
from a fjord system (Ameralik) in
southwest Greenland impacted by a
land-terminating glacier
• We compare our observations with the
neighbouring Godthåbsfjord, which
receives meltwater from both land-
and marine-terminating glaciers
• A large fraction of the seasonal
freshwater input is retained in the
fjord in summer and autumn, and is
exported primarily in winter
Supporting Information:
Supporting Information may be found in
the online version of this article.
Correspondence to:
A. E. Stuart-Lee,
alice.stuart-lee@nioz.nl
Citation:
Stuart-Lee, A. E., Mortensen, J., van
der Kaaden, A.-S., & Meire, L. (2021).
Seasonal hydrography of Ameralik: A
southwest Greenland fjord impacted
by a land-terminating glacier. Journal
of Geophysical Research: Oceans,
126, e2021JC017552. https://doi.
org/10.1029/2021JC017552
Received 6 MAY 2021
Accepted 7 NOV 2021
10.1029/2021JC017552
RESEARCH ARTICLE
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features (e.g., fjord bathymetry, freshwater sources, tides). This drives the need for studies into a range of fjords
across Greenland. Changes in marine-terminating glaciers are responsible for most of Greenland's contribution to
sea level rise in recent decades (King etal.,2020; Mouginot etal.,2019). The fjords in which these glaciers ter-
minate have received considerable research attention, with particular focus on subglacial discharge and its related
upwelling mechanism which contributes to the unique hydrography of these fjords (e.g., Mankoff etal., 2016;
Mortensen etal.,2020; Sciascia etal.,2013; Straneo etal.,2011).
Although fjords impacted by land-terminating glaciers represent a substantial remaining proportion of Green-
land's coast and key export routes for meltwater from the Greenland Ice Sheet to the ocean, few studies focus on
this type of fjord (e.g., Dmitrenko etal.,2015; Nielsen etal.,2010). One such example is Kangerlussuaq, a fjord
on the west coast (66.8°N, 51.5°W), which only receives glacial meltwater via river runoff. The inner part of
Kangerlussuaq is segregated from the ocean by a 100km long shallow outer section, almost decoupling the inner
fjord from coastal dynamics. As such, fjord hydrography is strongly determined by meltwater runoff in summer,
driving stratification and estuarine circulation, and by sea ice formation in winter, forming dense water through
brine release (Lund-Hansen etal.,2018; Monteban etal.,2020; Nielsen etal.,2010).
In addition, research has been carried out in the Young Sound/Tyrolerfjord system on the northeast coast (74.4°N,
20.4°W) which is also impacted only by meltwater runoff via land. Estuarine circulation resulting from this
runoff characterises this system in summer, while polynyas and tide-driven fjord-shelf exchange are drivers of a
two-layer circulation in winter that extends up to ∼150m depth (Bendtsen etal.,2014; Boone etal.,2017; Dmi-
trenko etal.,2015). Young Sound has a very shallow outer sill of ∼45m depth that is a topographic barrier to the
ocean (Rysgaard etal.,2003), and its location on the east coast means that it is impacted by different coastal water
masses (associated with the East Greenland Current) than those found on the west coast (Rysgaard etal.,2020).
Variation observed in seasonal climate, coastal water masses and other physical differences such as bottom to-
pography leads to a need for high resolution and seasonal studies of other fjords impacted by land-terminating
glaciers.
Here we describe for the first time the seasonal hydrography, inferred circulation patterns and meteorological
conditions of Ameralik, a fjord impacted by a land-terminating glacier, which is located next to Godthåbsfjord
on the southwest coast of Greenland (Figure1a). Transects from March–December 2019 and observations from
March 2020 provide a unique description of changing seasonal conditions in Ameralik. We compare our data
to observations from Godthåbsfjord, which, in contrast to Ameralik, is impacted by three marine-terminating
glaciers in addition to three land-terminating glaciers. The seasonal hydrography of Godthåbsfjord has been de-
scribed extensively (Mortensen etal.,2011,2013,2014,2018), providing a breadth of existing knowledge includ-
ing a baseline study on the surrounding water masses to aid the analysis of Ameralik. Additionally, hydrographic
surveys conducted in 2019 allow a closer comparison. We investigate the roles of land- and marine-terminating
glaciers in order to highlight fundamental differences between the two systems and contribute toward our under-
standing of potential future fjord transitions under glacial retreat.
2. Study Area and Methodology
2.1. Regional Setting
Ameralik is located on the southwest coast of Greenland close to Nuuk (Figure1a). The fjord is ∼75km long,
5–7km wide and has an area of ∼400km2. A ∼110m deep sill is found at the entrance to the fjord and the central
part is characterized by a sequence of deep basins reaching a maximum depth of ∼700m (Figure1b). The tidal
range for Nuuk is ∼1–5m (Richter etal.,2011). The fjord remains largely ice-free throughout the year, with sea
ice only found close to the river delta in the inner part of the fjord during winter. No glaciers terminate directly
in the fjord, though glacial meltwater is delivered via runoff from rivers. Meltwater is primarily supplied by the
glacial river Naajat Kuuat (Figure1a), which drains a catchment area of ∼356km2 of the Greenland Ice Sheet.
For 2012, discharge from the river was estimated as 0.78km3yr−1 (Overeem etal.,2015).
Godthåbsfjord (Nuup Kangerlua) is the neighbour fjord to Ameralik on the northern side (Figure1a). It has a
length of ∼190km and a surface area of 2,013km2 extending over several fjord branches and containing multiple
sills. The main sill is located at the entrance with a depth of ∼200m and the deepest point is 620m (Mortensen
etal.,2011,2018). In Godthåbsfjord, meltwater and glacial ice are delivered by three marine-terminating glaciers
and three land-terminating glaciers via rivers. Estimates from a regional climate model for freshwater input are

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18.4±5.8km3yr−1 for the marine-terminating glaciers, excluding solid ice discharge, and 7.5±2.1km3yr−1 for
the land-terminating glaciers (based on the period 2002 to 2012, Langen etal.,2015). Solid ice discharge from
the three marine-terminating glaciers is estimated at 7–10km3 w.e. yr−1 (Van As etal.,2014). Sea ice is present
seasonally in the innermost part of Godthåbsfjord (from near station GF13 inwards, Figure1a).
The coastal waters outside of Ameralik and Godthåbsfjord are characterized by distinct water masses (winter
mode waters: Rysgaard etal.,2020). The upper layer is composed of relatively cool and fresh southwest Green-
land coastal water (θ-S properties ∼0°C and 33) arriving from the south with an origin in the East Greenland
Current and runoff from Greenland. In summer 2016 this coastal water was identified in the upper 200m of the
water column at 64°N, close to Ameralik and Godthåbsfjord (Rysgaard etal.,2020). At greater depths, warmer
and more saline subpolar mode water of Atlantic origin is present, which is subdivided into upper subpolar
mode water (θ-S properties ∼6°C and 35) and deep subpolar mode water (θ-S properties ∼4°C and 34.7) (Lin
etal.,2018; Rysgaard etal.,2020). The thickness of the combined subpolar mode water layer varied between 0
and 600m along the southwest coast of Greenland in summer 2016 (Rysgaard etal.,2020). The seasonal presence
Figure 1. (a) Map of Ameralik and Godthåbsfjord. Standard CTD station locations are indicated by solid black circles. Selected stations are labeled in black (prefixed
with “GF” for Godthåbsfjord or “AM” for Ameralik). Other sites are labeled in blue: Nuuk, the Greenland ice sheet (“GrIS”), the weather station in Ameralik (“WS”),
and the river Naajat Kuuat (“NK”). The study area is identified on the inset map of Greenland. (b) Bathymetry section of Ameralik with approximate station positions
indicated.

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of cold and relatively saline Baffin Bay polar water (θ-S properties ∼−1.8°C and 33.6) of northern origin can
occasionally be observed in a diluted form outside the fjords (Rysgaard etal.,2020).
2.2. Sampling
Air temperature, photosynthetically active radiation (PAR), wind speed and wind direction data were measured
with 10min resolution in 2019 for Ameralik using an Onset weather station located on land in the inner part of
the fjord on the north side (64°13.42'N, 50°18.12'W, Figure1a). In its vicinity a SBE microcat mooring (SBE
37-SMP, SeaBird) was fixed to the bedrock at a mean depth of ∼6m, just outside the intertidal zone, measuring
the surface layer water temperature, salinity and pressure with 10min resolution. Air temperature and wind speed
were obtained from the meteorological station in Nuuk (Asiaq, Greenland Survey).
Due to practical limitations it was not possible to assess potential rotational effects in Ameralik. However, ear-
lier work based on cross-fjord sampling in Godthåbsfjord found limited cross-fjord variation with the dominant
flow being in the along-fjord direction (Mortensen etal.,2014). As Ameralik is narrower than Godthåbsfjord,
cross-fjord variation is presumed to also be limited, resulting in the focus on the along-fjord gradient. Seasonal
measurements were made at 12 standard stations in Ameralik spaced between 3 and 13km from one another
(AM1 to AM12 in Figure1a) in May, July and September 2019. Longer term fjord sampling was also carried
out at monthly intervals from March–December 2019 at selected stations (AM3, AM5, AM7, AM10, AM11 and
AM12) and in March 2020 at station AM5.
Additionally, sampling was conducted at 13 standard stations in Godthåbsfjord (GF1 to GF13 in Figure1a) in
May, July and September 2019. Favourable ice conditions in the inner fjord during the September campaign al-
lowed the sampling of 4 further standard stations (GF14 to GF17). Longer term fjord sampling in Godthåbsfjord
was also carried out at monthly intervals from February to December 2019 at selected stations from GF5 and
inwards.
At every station, depth profiles of conductivity, temperature and pressure were collected using a SeaBird SBE-
19plus CTD and averaged over 1m vertical depth intervals. Sensors were calibrated annually by the manufacturer
and salinity precision was typically within the range of 0.005–0.010. Sampling took place aboard the Greenland
RV Sanna and Avataq, and the commercial Greenland vessels Polar Dive and Tulu. For comparison with previous
field programs, potential temperature (ITS-90) and practical salinity are used throughout the text.
Freshwater content (FWC) represents the portion of the water column composed of freshwater, expressed in me-
ters. This was calculated for salinity profiles with 1m resolution at depth ranges 0–50, 50–200 and 200–500m
at station AM5 according to the equation:


  ref
ref
FWC dz
za
zb
S Sz
S
where z is the depth, a and b are the top and bottom depths, S is the measured salinity, and Sref is the reference
salinity, which was set at 33.3. This value is the maximum salinity measured in Ameralik across the sampled
period (at station AM5 in March 2019).
The stratification index (φ, J m−3) represents the energy required to completely mix the water column (Simp-
son,1981) and was calculated according to the equation of MacKenzie and Adamson(2004):

 

 

0
1dz
1
hgz
h
integrating from a constant depth h to the sea surface and where ρ is the measured density at the vertical coor-
dinate z,

E
is the mean density from the sea surface to h, and g is acceleration due to gravity (9.81ms−2). To
compare differences in the surface layer, this calculation was based on density profiles from the upper 50m for
all stations except AM12, for which the upper 36m was used (maximum depth of the station). All processing of
data was done using the open-source programming language R (R Core Team,2013).

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3. Results
3.1. Weather Observations
Data from the weather station in the inner part of Ameralik (Figure1a) show low incoming solar radiation in
the winter of 2019, with a mean PAR of ∼16μmolm−2s−1 in January (Figure2a). Air temperatures in winter
reached a low of −18°C (Figure2c). The gradual increase in incoming radiation during spring resulted in positive
monthly mean temperatures starting from April and peaking in July at 12°C. Compared to similar measurements
collected in Nuuk in 2019, air temperatures in the inner part of Ameralik were colder in winter and warmer in
summer (Figure2c). The mean temperature in January was −8.3°C at the Ameralik station, and −6.4°C in Nuuk,
Figure 2. Weather conditions for Ameralik and Nuuk in 2019. Weekly mean values (solid circles, thick lines), and daily
means (thin lines) for (a) photosynthetically active radiation at Ameralik weather station, (b) sea surface temperature (black)
and sea surface salinity (red) at Ameralik mooring, (c) air temperature, and (d) wind speed at Ameralik weather station
(black) and Nuuk weather station (blue). Month labels on the x-axes of (a–d) appear in the middle of the month. (e) Quarterly
windroses for Ameralik.

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and in June these were 10.3°C and 6.5°C respectively. This is in line with similar observations in the region
showing a clear land-ocean gradient (Abermann etal.,2019).
Distinct seasonal changes were also found in the wind patterns in Ameralik, with the highest mean daily wind
speeds occurring between November and April. Wind speeds further out of the fjord were generally higher, as
can be seen from a comparison with Nuuk, close to the coast (Figure2d). Throughout the year, wind was usually
oriented along the fjord axis, as observed in other Arctic fjords (e.g., Svendsen etal.,2002), with the steep moun-
tainous terrain of Ameralik contributing with orographic effects (Figures1a and2e). From January to March,
and from October to December (roughly corresponding to winter months), winds blew predominantly out-fjord
(easterly wind) throughout the day (Figure2e). From April to September, as the land became warmer than the
sea, the dominant wind direction was in-fjord (westerly wind) (Figure2e). Transitions between these two modes
took place during April and late August to September. The summer winds were less uni-directional and changes
in wind direction occurred during the day due to differential heating between land and sea. Generally there was
in-fjord wind during the day and weaker out-fjord wind at night.
3.2. Seasonal Hydrographic Observations in Ameralik
Owing to its mostly glacial source, freshwater runoff to the fjord is highly seasonal and increases approximately
in line with air temperature once above 0°C. This corresponds to little to no runoff between October and April
(Van As etal.,2014). In March 2019, air temperature remained well below 0°C, corresponding to low freshwater
runoff. Under these conditions, increased wind speeds, together with tides, promoted mixing of the water column.
This is reflected in a relatively uniform cold (∼0°C) and saline (∼33.1) water column with weak stratification and
little horizontal or vertical variation (Figures3a and3b).
As air temperature and insolation rose through spring and summer, the surface water warmed and produced an
along-fjord surface gradient with temperatures increasing from outer to inner fjord (Figures3c and3e). Mooring
data demonstrate the time lag between sea surface layer temperature and insolation (Figures2a and2b). Sea sur-
face layer temperature at the mooring (∼6m depth, depending on the tide) increased quickly in May, with a rise of
7.5°C in the weekly mean. In May, a shallow thermocline started to develop in the upper 10m, most prominently
from the midfjord (AM5) to the innermost station (AM12). In this range the mean potential temperature of the
upper 10m layer was 1.9°C and the mean salinity was 32.8. At the mouth of the fjord (AM1 and AM2), vertical
gradients near the surface were limited.
In subsequent months, increased freshwater runoff further strengthened the surface stratification through the
establishment of a thin layer of relatively fresh (mean salinity <31) water in the upper 10m of the central and
inner fjord stations (AM5 to AM12). Driven by the estuarine circulation, which results in a net out-fjord flow in
the surface layer, the freshwater runoff originating in the inner fjord was transported out-fjord. By July, following
high levels of freshwater runoff, this surface layer was well defined along Ameralik with salinity as low as 6 in
the inner part of the fjord (station AM12) and a strong halocline in the upper 6m of the central and inner fjord
stations (AM5 to AM12, Figures3e and3f). The upper 10m layer of this range had a mean potential temperature
of 8.0 ◦C and mean salinity of 28.6. The intermediate depths (50–200m) freshened and warmed during this peri-
od (Figures3c–3f,4a and4b), which we explain in Section4.1.
As September arrived, the air temperatures dropped below those of the surface waters (Figures2b and2c) and
freshwater input will have declined strongly (Van As etal.,2014), leading to higher salinity in the surface layer
and a less pronounced halocline. Together with increased winter storms (evidenced by higher daily mean gust
speeds in the winter months, FigureS1), this resulted in a much weaker surface stratification throughout the fjord
by the end of the year (Figures3i and3j). The upper 10m layer from station AM5 to AM12 had a mean potential
temperature of 6.3°C and mean salinity of 30.2 by September. At intermediate depths (50–200m) we observe a
gradual deepening of isopycnals during autumn (September–November, Figures3g–3j), determined primarily by
the changes in salinity (dashed line representing the 200m depth in Figures4b and4c).
3.3. Retention of Summer Accumulated Freshwater in Ameralik
To assess changes in freshwater, freshwater content (FWC) was calculated for a station in the central fjord (AM5)
using the maximum salinity in Ameralik in March 2020 as the reference value. A significant freshening took

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Figure 3. Bimonthly potential temperature and practical salinity length sections of upper 500m of Ameralik from March to November 2019, from outer fjord (left) to
inner fjord (right). March and November data are from long term Ameralik monitoring; May to September data are from the seasonal campaigns with higher horizontal
spatial resolution.

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place at station AM5 between June and August, with an increase in FWC of
the upper 500m layer of 4.4m (Figure5). This was followed by a decrease of
1.2m between August and December. Considering individual layers during
this period of decline in the second half of the year, the surface layer (0–50m)
FWC decreased by 2.1m, while that of the intermediate layer (50–200m) in-
creased by 0.7m, and that of the deep layer (200–500m) increased by 0.3m.
This shows that a large fraction of the freshwater discharged during the sum-
mer months remained within the fjord rather than being directly exported.
3.4. Winter Fjord Water Renewal in Ameralik
The deep water (below 400m) is fairly isolated owing to the combination
of a shallow entrance sill (∼110m) and deep basin (Figure1b). As such,
this water is decoupled from the seasonal changes observed in the upper wa-
ter column and its properties remained stable for much of 2019 (Figure4).
Due to diffusion processes the density of the basin water gradually lowers
(Figure4d), reducing the density difference between the coastal water and
the fjord. In this way, the basin water becomes preconditioned for dense
coastal inflows, whereby coastal water enters over the sill and replaces the
resident fjord water. Mid-fjord measurements are not available for January
and February 2019, but we identify dense coastal inflow in late winter/early
spring 2019 from the increase in potential density anomaly of 0.03kg m−3
at 400 m between March and May (Figure4d) and associated increase in
salinity of 0.26 (Figure4b). This increase cannot be attributed to the process
of brine rejection due to the lack of sea ice and drifting sea ice in Ameralik
during winter. Nor can wind forcing or convection be the primary cause as
this would result in decreased salinity. Winter dense coastal inflow has also
been observed in the neighbouring Godthåbsfjord (Mortensen etal.,2018).
Following this period of deep water renewal in Ameralik, the density of the
basin water was at its highest, and further dense coastal inflow events are not
observed during the summer months.
There was a substantial decrease of 1.9m in FWC between December 2019
and March 2020 (Figure5), which may be representative of an annual pattern,
i.e., a large freshwater export occurring each winter. If this is the case, the
period can be characterized by a flushing of the summer accumulated fresh-
water throughout the fjord. From the approximated surface area of ∼400km2
and the difference of 1.9m in FWC at AM5 between December 2019 and
March 2020, we estimate an export of ∼0.8km3. This is very close to the
estimated annual river discharge of 0.78km3 reported in Section 2.1. The
estimated export is most pronounced in the intermediate layer (50–200m),
with a 1.5m decrease between December 2019 and March 2020. We hypothesise that a fraction of the meltwater
discharged to the surface layer is retained within the fjord system and only flushed out of the intermediate layer
after the summer, indicating that the winter period plays an important role for the freshwater export.
3.5. Water Masses in Ameralik and Godthåbsfjord
Potential temperature and salinity (θ-S) curves from a selection of stations in Ameralik and Godthåbsfjord in
July and December 2019 are shown in Figure6. Changes in insolation and volumes of meltwater input result in
a large difference in temperature and salinity ranges between summer and winter. In July, the θ-S curves show
the relatively warm and fresh summer surface water from the surface layers of the inner fjords (Figure6a). This
summer surface water originated from runoff (i.e., freshwater runoff to the surface layer) and net precipitation,
which was subsequently warmed by solar radiation. In Godthåbsfjord, a prominent dip in temperature and salinity
identifies the body of cool and fresh subglacial water below the summer surface water in the inner part of the fjord
Figure 4. Time series of water properties at station AM5 in 2019: (a)
potential temperature at 100, 200 and 400m, (b) practical salinity at 100, 200
and 400m, (c) potential density anomaly at 100 and 200m, and (d) potential
density anomaly at 400m. Line types represent depths: dotted for 100m,
dashed for 200m, and solid for 400m. Note the difference scales used in (c)
and (d) for potential density anomaly.

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(Figure6a). This subglacial water, which is not found in Ameralik, has its origin in the subglacial discharge of
freshwater discharged at the grounding line of marine-terminating glaciers. The discharge undergoes modifica-
tion by entrainment as it ascends toward the surface, and then by cooling from the ice mélange as it is transported
Figure 5. Monthly Freshwater Content (FWC, m) at AM5 in Ameralik from March 2019 to March 2020. Calculated with a
practical salinity reference value of 33.3.
Figure 6. Potential temperature and practical salinity observations from selected stations in Ameralik (dashed lines) and Godthåbsfjord (solid lines) in (a) July, and (b)
December 2019. Each line represents the depth profile from one station. The July plot is cropped to exclude observations of practical salinity below 27 and potential
temperature above 9°C. Approximate positions of coastal (Rysgaard etal.,2020) and fjord (Mortensen etal.,2011) water masses are indicated with acronyms: BBPW,
Baffin Bay polar water; CW, southwest Greenland coastal water; dSPMW, deep subpolar mode water; uSPMW, upper subpolar mode water; SgW, subglacial water;
SrW, sill region water; sSW, summer surface water; wSW, winter surface water; BW, basin water. The gray basin water rectangles indicate water range in 2019 below
400m. The gray dashed lines are isopycnals.

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away from the glacier, and ends up below the summer surface layer (Bendtsen etal.,2015; Mankoff etal.,2016;
Mortensen etal.,2020).
The layer below the subglacial water contained sill region water, an intermediate water mass which originates
in the outer sill region where tidal-induced diapycnal mixing takes place between a number of near surface
water masses (i.e., summer surface water, subglacial water and coastal water) (Mortensen etal.,2011). In God-
thåbsfjord, sill region water can be identified by the temperature maximum relative to the cooler subglacial water
layer found above (Mortensen etal.,2011). Because Ameralik does not contain subglacial water, the profiles lack
the corresponding subsurface temperature minimum from which to identify the sill region water. It can however
be approximated from the overlap in properties with sill region water in Godthåbsfjord (Figure6a). The similarity
of these properties suggests that this is the same water mass, and that the same mechanism is therefore involved
in its formation in Ameralik as in Godthåbsfjord, which is further discussed in Section4.1.
Below the layer containing sill region water was the relatively cool and saline basin water, identified in Figure6
with gray boxes. This occupied the water column down to the bottom, remaining almost stagnant for most of the
year with intermittent periods of renewal during winter.
In winter, cooling and reduced freshwater runoff was responsible for the formation of winter surface water and
fjord properties were dominated by basin water, a fjord water mass with close connection to the coastal water
masses (Figure6b).Observations from sampled central fjord stations in March 2019 show that the mean prop-
erties of the upper 10 m layer were slightly cooler and more saline in Ameralik (−0.1°C, 33.1) than in God-
thåbsfjord (0.3°C, 32.9).
3.6. Fjord Comparison of Upper Water Column Properties
The seasonal hydrography of Godthåbsfjord is well documented (Mortensen etal.,2011,2013,2018,2020) and
the focus here is on the comparison with Ameralik.
Figure7 presents the mean potential temperature of the upper 50m layer at each station through the studied
months. Temperatures near the shared mouth region of the two fjords remained similar, but further in-fjord di-
verged considerably. In May, at the start of the melt season, the upper 50m layer of Ameralik (mean of stations
AM1 to AM12) was 0.6°C cooler than in Godthåbsfjord (mean of stations GF1 to GF13), which relates to the
differences in entrance sill depth and associated basin water temperatures. As discussed below in Section4.2, the
basin water of Ameralik in 2019 was cooler than that of Godthåbsfjord. During winter flushing, a portion of the
basin water was displaced upwards (e.g., Mortensen etal.,2018), consequently affecting the temperature of the
upper water layers. The lower temperatures in the basin water of Ameralik and inflow of cooler water are both
likely to have contributed to the colder subsurface layer compared to Godthåbsfjord. During winter and spring,
icebergs in Godthåbsfjord remained mostly trapped in the innermost fjord by sea ice (i.e., in the ice mélange),
which may have limited their cooling influence at that time. However, large changes in surface layer properties
between the studied months show the influence of the strong meltwater input in Godthåbsfjord (composed of
runoff, subglacial freshwater discharge and net precipitation) as well as the presence of large quantities of ice-
bergs further out-fjord (observed during fjord sampling). As a result, by July the upper 50m layer of Ameralik
was warmer than the upper 50m of Godthåbsfjord, and by September the difference in mean temperature of the
upper 50m was 2°C (Figure7).
The extra freshwater input in Godthåbsfjord does not lead to increased overall stratification: the stratification
index is higher in Ameralik than in Godthåbsfjord in the mid- and outer fjord in July (Figure8). This can be ex-
plained by the presence of subglacial discharge in Godthåbsfjord, whereby the freshwater released at depth forms
buoyant plumes that entrain surrounding ambient water, bringing deep fjord water toward the surface and mixing
the water column (Bendtsen etal.,2015). The subglacial water forms an out-fjord flow below the shallow surface
layer that originates from runoff (∼10–30m depth range, Figures9c and9e). In this way, subglacial discharge
has an impact on the vertical structure of the water column throughout the fjord. Increases in runoff can have a
similar effect by causing a thinning of the surface layer (Bendtsen etal.,2014). In May, the surface layer in Am-
eralik was shallower than in Godthåbsfjord, but by July, as freshwater input increased, this layer was shallower in
Godthåbsfjord than in Ameralik (Figures10b and10c).

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4. Discussion
4.1. Fjord Circulation Comparison
By winter, seasonal change in Ameralik led to the disappearance of the summer stratification, whereas in God-
thåbsfjord some stratification remained (Figure10a). These seasonal changes are influenced by a combination
of mixing mechanisms including tides and dense coastal inflows, which in Ameralik resulted in a flushing of
the fjord, as has been inferred from the increasing basin water density discussed in Section3.4. Godthåbsfjord
also experiences dense coastal inflows, but in Godthåbsfjord the deep water does not completely renew (e.g.,
Mortensen etal.,2018). The presence of sea ice also contributes to the perseverance of stratification in God-
thåbsfjord by providing a barrier to wind mixing (Meire etal.,2015). As observed in Ameralik, it may be that
during the winter period (when dense coastal inflow is active) Godthåbsfjord also undergoes a large export of
summer accumulated freshwater. The FWC calculations in 2008–2009 show that FWC at intermediate depths
(30–277m) dropped from 4.1m in November to 1.5m in May (based on a reference salinity of 33.56, Mortensen
etal.,2011).
In the intermediate water layer (50–200m) of Godthåbsfjord in July there was an inflow of a warm tongue ex-
tending from the fjord entrance (Figure9c). From station GF5 inwards this can be observed beneath the cooled
layer of subglacial water (∼10–30m) that is itself below the warmer surface layer (∼0–10m). This is referred
to as intermediate baroclinic circulation by Mortensen etal.(2011) and develops with a compensation out-flow
below, lowering the isopycnals in the fjord. This circulation was later supported by direct current measurements
(Mortensen etal.,2014). It is present year-round in Godthåbsfjord (Figures11b and11d), driven by density dif-
ferences between the inner and outer fjord and the shelf/coast. It is the most dominant circulation in summer when
the combination of tidal mixing in the outer sill region and warming and freshening of surface fjord water results
in the outer fjord water becoming less dense than the inner fjord (Mortensen etal.,2014).
We hypothesise that the intermediate baroclinic circulation is also present in Ameralik. Ameralik also displayed
steady warming and freshening in its intermediate layer during summer (Figures 3e and 3f) and associated
Figure 7. Mean potential temperature in the upper 50m depth layer of each station in (a) Ameralik, and (b) Godthåbsfjord in
May, July and September 2019.

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deepening of the isopycnals. In addition, mid-fjord (station AM5) potential density anomaly measurements show
that there was greater change between May and December in intermediate depths (100 and 200m, Figure4c) than
deeper in the water column (400m, Figure4d). The change in density from May to December observed at 400m
at AM5 (−0.024kg m−3) is indicative of diffusion processes and is an order of magnitude smaller than at 200m
(−0.325kg m−3) and 100m (−0.514kg m−3) depths, indicating the existence of another exchange mechanism
at 100 and 200m depths. This supports our hypothesis, which is further evidenced by the finding made in Sec-
tion3.5 that sill region water was present in both outer and inner fjord stations of Ameralik and Godthåbsfjord.
We hypothesise that, after forming in the outer sill region, this water mass was transported into the fjord by
the intermediate baroclinic circulation, as has been verified in Godthåbsfjord through current measurements
(Mortensen etal.,2014).
4.2. Impact of Sill Depth on Bottom Water Properties
A comparison of deep water properties reveals another important difference between these two fjords. Between
50 and 400m, Ameralik was fresher (by 0.2) and cooler (by between 0.7 and 1.1°C) than Godthåbsfjord for each
of the studied months (May, July and September). This difference also applied to the water below 400m, as
indicated by the gray rectangles in Figure6. The difference in deep water properties is related to the sill depth,
Figure 8. Stratification index (φ) for upper 50m water depth layer of Ameralik (stations AM3 to AM12) and Godthåbsfjord
(stations GF3 to GF13).

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which determines the inflow of coastal water and differs between the two fjords. The entrance sill of Ameralik is
∼110m deep, compared to the ∼200m deep entrance sill of Godthåbsfjord. As a result, Ameralik receives less
of the deeper, warmer and more saline subpolar mode water from the coastal region than Godthåbsfjord does.
As this water makes its way into the fjord and mixes with local waters it eventually becomes part of the basin
water. As such, the reduced inflow of subpolar mode water in Ameralik compared to Godthåbsfjord can explain
the cooler and fresher deep water observed in Ameralik. This has important implications for the ecology due to
distinct environmental preferences of species, as well as variation in the species transported in these different
water masses (e.g., Grainger,1963; Hirche,1991; Hirche & Mumm,1992).
4.3. Implication of Fjord Comparison
Comparing Ameralik with Godthåbsfjord demonstrates how the absence of marine-terminating glaciers, and
thus of subglacial freshwater discharge, impacts the surface layer of the fjord (0–50m), with Ameralik found
to be more stratified on average than Godthåbsfjord in the summer (Figure8). Increased summer stratification
may be reflected in the future of fjords undergoing a retreat of glaciers onto land. This is in line with modeling
predictions (e.g., Torsvik etal.,2019). The upwelling mechanism resulting from the subglacial discharge plumes
has further implications for the nutrient distribution near the termini, which sustains primary production (Hop-
wood etal.,2018; Kanna etal.,2018; Meire etal.,2017) and extends support to the wider food web, including
Figure 9. Potential temperature and practical salinity length sections of the upper 500m of Godthåbsfjord in May, July and September 2019, from outer fjord (left)
to inner fjord (right). Note that the length represented is greater in the September section, when favourable ice conditions allowed inner fjord stations GF14-17 to be
sampled.

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marine mammals and seabirds (Lydersen etal.,2014; Urbanski etal.,2017). However, despite the higher summer
stratification, the absence of a marine-terminating glacier does not necessarily mean a less dynamic fjord. We
argue that there are three circulation modes in Ameralik, illustrated in Figures11a and11c. Dense coastal inflows
across the sill during the winter of 2019–2020 had a major impact in the flushing of Ameralik through water
renewal and induced internal upwelling. This prevented basin water from remaining stagnant through the whole
year and contributed to the return of a weakly stratified state in winter. Meanwhile, the surface layer of Ameralik
was modified through estuarine circulation (driven by freshwater from river runoff) and wind forcing. Tides are
likely to have had an impact on mixing in Ameralik, with its location in the Davis Strait as one of the regions of
Greenland's coast with the highest tidal ranges (Padman etal.,2018) and its shared entrance with Godthåbsfjord,
which is highly turbulent (Mortensen etal.,2018). The tidal-induced mixing in the outer sill region most likely
contributed to the setup of an intermediate baroclinic circulation, which resulted in the exchange of water at
intermediate depths and consequently plays an important role in redistributing heat and freshwater in the fjord
(Mortensen etal.,2014).
The circulation activity in fjords impacted only by land-terminating glaciers is set by boundary conditions includ-
ing the sill depth, fjord geometry, coastal water masses, tidal currents, annual freshwater input (glacial water and
net precipitation) and regional climatic conditions, all of which vary considerably across the fjords of Greenland.
In contrast to the bottom water renewal observed in Ameralik, long term mooring data from the Young Sound/
Tyrolerfjord system on the northeast coast of Greenland show that bottom water renewal did not occur in the
period between 2004 and 2014 (Boone etal.,2018). The relatively shallow (∼45m) outer sill strongly restricts
deep water renewal. Ongoing freshening in the coastal water in East Greenland further reduces the chance that
it will exceed the density of the fjord basin water, which is necessary for coastal water to be able to reach these
depths (Boone etal.,2018; Sejr etal.,2017).
Figure 10. Potential density anomaly in upper 50m water depth layer of Ameralik and Godthåbsfjord in (a) March, (b) May, (c) July, and (d) September 2019. Note
that different scales are used for the x-axes.

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5. Summary and Conclusions
Ameralik, in southwest Greenland, represents the stage of a fjord after its glaciers have retreated from a ma-
rine-terminating to a land-terminating position. In this study we provide the first description of its hydrography,
and compare our findings with the neighboring Godthåbsfjord, which is impacted by both land- and marine-ter-
minating glaciers.
The absence of a marine-terminating glacier, and therefore of glacial ice and subglacial discharge, has implica-
tions for the hydrography and circulation. In 2019, spring and summer months in Ameralik were characterized
by the transition from a weakly stratified fjord to a fresher, highly stratified fjord with a strong halocline and an
estuarine circulation resulting from freshwater runoff. We found that a large fraction of the freshwater input is re-
tained inside the fjord during the summer and autumn months, which we propose occurred through intermediate
baroclinic circulation. During this period the upper 50m water layer was considerably warmer in Ameralik than
in Godthåbsfjord. Autumn and winter represented a steady return toward the pre-spring conditions, as freshwater
runoff was strongly reduced, and export of summer accumulated freshwater from the fjord occurred, which we
propose was related to coastal inflows. This resulted in flushing of the fjord and restored the system to a weakly
stratified state. The shallower main sill of Ameralik with respect to that of Godthåbsfjord resulted in the intrusion
of less of the subpolar mode water that is warmer and more saline compared to the overlying southwest Greenland
coastal water. This produced differences in the fjord water properties which may be important for fjord ecology.
Tides are likely to play a major role in mixing in the fjord, with tidal-induced mixing contributing to the setup
of an intermediate baroclinic circulation in the fjord, as identified from the downward temporal movement of
isopycnals at mid-depths and the inferred in-fjord transportation of sill region water in Ameralik. This case study
demonstrates the importance of physical features, such as bathymetry and glacier type, as well as coastal water
masses for the hydrography of Greenland fjords.
Figure 11. Conceptual diagrams of circulation modes and coastal water masses during summer and winter in Ameralik (a, c) and Godthåbsfjord (b, d). Thick black
arrows represent freshwater input (surface runoff and subglacial meltwater discharge). Thin black arrows represent entrainment into the subglacial plume. Thin colored
arrows represent net effects of circulation modes: yellow for estuarine circulation, red for intermediate baroclinic circulation, gray for subglacial circulation and blue for
dense coastal inflows.

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Data Availability Statement
Processed CTD, mooring and weather data are available at the World Data Center PANGAEA (Stuart-Lee et al.,
2021a, 2021b, 2021c).
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Acknowledgments
L. Meire was funded by research program
VENI with project 016.Veni.192.150
from the Dutch Research Council (NWO).
Meteorological data from Nuuk were
provided by Asiaq Greenland Survey,
Nuuk, Greenland. We would like to thank
Flemming Heinrich, Else Ostermann,
Thomas Juul-Pedersen and the crew of
RV SANNA, Peter Rosvig Pedersen of
the Polar Diver, Anders Pedersen and the
crew of the Tulu for field assistance. This
study received financial support from the
Greenland Climate Research Centre. This
study was conducted in collaboration with
the MarineBasis Nuuk monitoring pro-
gram, part of Greenland Ecosystem Moni-
toring (GEM), and forms a contribution
to the Arctic Science Partnership (ASP).
Data from the Greenland Ecosystem
Monitoring Programme (www.g-e-m.dk)
were provided by the Greenland Institute
of Natural Resources, Nuuk, Greenland.

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