Figure 9 - uploaded by S. Stammerjohn
Content may be subject to copyright.
(a) Changes in sea-ice area (km 2 ) derived from DMSP SSM/I 85 GHz data, in comparison with net volume fluxes (m 3 /s) in/out of: (b) box 1, (c) box 2, and (d) box 3. Data gaps in sea-ice area occur when the ice-edge retreats into the box (therefore the box is not completely covered), while data gaps in the net volume fluxes occur when the sides of the box are ice-free (therefore the flux cannot be determined). Daily volume fluxes are shown by thin lines, 5-day mean fluxes are shown by thick lines, and error bars (1 sigma) are indicated by the (darkest) shaded region bracketing the curve. Vertical shaded panels are periods of ice-edge advance (light shading) and retreat (dark shading).
Source publication
The seasonal evolution of sea-ice extent, concentration, and drift in the western Antarctic Peninsula (WAP) region, along with regional atmospheric synoptic variability, are described for a winter period (1992) when sea-ice advance and retreat were both anomalously early. Daily time series of winds, opening and closing of the sea-ice cover, and vol...
Similar publications
This work presents snapshot simulations of the late 20th and late 21st century Antarctic climate under the RCP8.5 scenario carried out with an empirically bias-corrected global atmospheric general circulation model (AGCM), forced with bias-corrected sea-surface temperatures and sea ice and run with about 100-km resolution over Antarctica. The bias...
The atmospheric signals associated with El Niño are weak in the northern sector of the Antarctic Peninsula. This is revealed by the monthly average of the precipitation, the atmospheric pressure and the minimum air temperature registered by the Antarctic Chilean stations: O’Higgins, Prat and Frei. The signal is clearer in the precipitation that sho...
Citations
... In that case, our results indicate that the non-ice-edge bloom is beginning later over time (Fig. 4), implying that the later phytoplankton accumulation timing is not directly associated with changes in sea ice dynamics. Fluctuations in sea ice dynamics are linked to oscillations of the Southern Annular Mode (SAM) and changes in wind speed and direction (Stammerjohn et al. 2003, Turner et al. 2013. Our results show increasing wind speed over the offshore waters from the northwest, consistent with a long-term trend toward a positive SAM, without a concurrent change in wind direction (Fig. S13). ...
Climate change is altering global ocean phenology, the timing of annually occurring biological events. We examined the changing phenology of the phytoplankton accumulation season west of the Antarctic Peninsula to show that blooms are shifting later in the season over time in ice-associated waters. The timing of the start date and peak date of the phytoplankton accumulation season occurred later over time from 1997 to 2022 in the marginal ice zone and over the continental shelf. A divergence was seen between offshore waters and ice-associated waters, with offshore bloom timing becoming earlier, yet marginal ice zone and continental shelf bloom timing shifting later. Higher chlorophyll a (chl a) concentration in the fall season was seen in recent years, especially over the northern continental shelf. Minimal long-term trends in annual chl a occurred, likely due to the combination of later start dates in spring and higher chl a in fall. Increasing spring wind speed is the most likely mechanism for later spring start dates, leading to deeper wind mixing in a region experiencing sea ice loss. Later phytoplankton bloom timing over the marginal ice zone and continental shelf will have consequences for surface ocean carbon uptake, food web dynamics, and trophic cascades.
... One of the main mechanisms put forward previously, based on an energy budget analysis from observations, is that upwelling and associated warm surface waters accelerate sea-ice melt 6,7 . An alternative mechanism, based on connections identified in observations, has the asymmetry caused by processes in the atmosphere rather than the ocean, with the semi-annual oscillation of the atmospheric low-pressure trough that surrounds the Antarctic continent creating patterns of convergence and divergence of Antarctic sea ice that favour fast ice retreat [8][9][10][11][12] . In this article, we systematically investigate the physical mechanism responsible for this asymmetry using observations and a range of climate models. ...
The mean seasonal cycle of Antarctic sea-ice extent is asymmetric, with the period of ice retreat being approximately two months shorter than the period of ice advance. This feature is largely consistent in observations from year to year and across different satellite products. The asymmetry is also broadly reproduced by comprehensive climate models across generations from CMIP3 to CMIP6, with limited impacts from internal variability. Using a range of idealized climate models of varying complexity, we show that the seasonal cycle in top-of-atmosphere incident solar radiation drives the asymmetry. Because insolation in southern high latitudes departs from a sinusoid by having a narrow peak of intense brightness in summer and a long period of low light in winter, there is rapid summer ice retreat and gradual winter ice advance. This simple physical explanation is markedly different from those proposed in previous studies.
... Throughout the year, the Antarctic SIE expands and retracts anomalously due to atmospheric and oceanic processes. These processes include advection of temperature by the meridional winds (Stammerjohn et al., 2003;Raphael, 2007); wind transport (Assmann et al., 2005;Holland and Kwok, 2012); Ekman transport (Hall and Visbeck, 2002;Sen Gupta and England, 2006); snowfall (Eicken et al., 1995;Sturm and Massom, 2009); ocean heat flow (Gordon, 1981;Andreas and Ackley, 1982); transient systems (Wang et al., 2014;Matear et al., 2015;Turner et al., 2020) and modes of climate variability (Lefebvre and Goosse, 2008;Yuan and Li, 2008;Pezza et al., 2012;Simpkins et al., 2012;Raphael and Hobbs, 2014;Pope et al., 2017). ...
... The focus of the present study is the southern winter, as it is the period in which the incursion of cold polar air over the Amazon presents the greatest frequency (Ricarte et al., 2015). We found that in most cases, the retraction (expansion) extremes of SIE HF in the sectors are preceded or followed by expansion (retraction) extremes, indicating that these extremes can be generated by the same transient system, since the high-frequency variability of sea ice seems to be associated mainly with extratropical cyclones (Enomoto and Ohmura, 1990;Stammerjohn et al., 2003). In addition, there were no consecutive retraction extreme events, as well as no expansion events. ...
... The high-frequency variability of SIE seems to be mainly associated with the mechanical action of winds associated with extratropical cyclones (Enomoto and Ohmura, 1990;Stammerjohn et al., 2003), while the heating or cooling of the surrounding atmosphere is less relevant (Eicken, 2003). The dynamic and thermodynamic explanations associated with the oceancryosphere-atmosphere interaction are outside the focus of the present work and will be presented in a future study. ...
The cold air incursion over South America is associated with the frontal systems generated in the Antarctic region, and sea ice cover plays an important role in its formation. Little is known about how the high‐frequency variability of the coupled ocean–cryosphere‐atmosphere system affects weather conditions in South America, especially in the Amazon region ‐ in tandem with the largest tropical forest on the planet and a key region of the global climate system. The results presented here suggest that the high‐frequency variability of the expansion of Antarctic sea ice extent (SIE) extremes, in the Ross Sea and Indian Ocean, modulate the cold air incursion over the Amazon in the southern winter 4 and 2 days after the expansion of SIE extremes, respectively. The SIE extremes can couple with the atmosphere, inducing Rossby waves that propagate and undergo amplification downstream from the Ross Sea and Indian Ocean during such extremes. In this way, the atmospheric wave train acquires a more southern spread over South America, reaching tropical latitudes after the SIE extremes. In non‐SIE extreme periods, the atmospheric wave train has a more zonal spread and reaches only the extratropical latitudes of the continent.
... Besides, it is also worth noting the discrepancy between the observed and simulated Antarctic sea ice trends and its potential effects on Southern Ocean heat uptake. Since the satellite era, Antarctic sea ice extent has exhibited a slight but statistically significant increase over more than three decades [e.g., Comiso and Nishio (2008)], which has been attributed to a variety of factors such as the El Niño-Southern Oscillation (Stammerjohn et al. 2003), the Interdecadal Pacific Oscillation (IPO) ) and/or the Amundsen Sea Low (Turner et al. 2015), the Atlantic Multidecadal Oscillation (AMO) (Li et al. 2014), natural variability of Southern Ocean convection (Zhang et al. 2019) and pole-to-pole teleconnection (Liu and Fedorov 2019). In austral spring 2016, Antarctic sea ice extent has experienced an abrupt drop (Turner et al. 2017) due to a combination of tropically forced and internal Southern Hemisphere atmospheric variability (Stuecker et al. 2017;Meehl et al. 2019;Purich and England 2019). ...
Atmospheric ozone concentrations have dramatically changed in the last five decades of past century. Herein we explore the effects of historical ozone changes that include stratospheric ozone depletion on Southern Ocean heat uptake and storage, by comparing CESM1 large ensemble simulations with fixed-ozone experiment. During 1958–2005, the ozone changes contribute to about 50% of poleward intensification of the Southern Hemisphere westerly winds in historical simulations, which intensifies the Deacon Cell and residual meridional overturning circulation, thus contributing to heat redistribution in the Southern Ocean. Heat budget analysis shows that, in response to historical ozone changes, heat is taken up between 50 and 58 °S mainly through changes in sensible heat flux, shortwave radiation flux, and the flux due to seasonal sea ice formation and melt. A major part of the absorbed heat, however, is redistributed equatorward primarily through Eulerian mean ocean heat transport such that ocean heat storage peaks at lower latitudes, around 44 °S. The ozone-induced interior warming contributes to about 22% of the historical Southern Ocean warming over 1958–2005. Poleward of 62 °S where a subsurface temperature inversion occurs, shoaling isopycnals lead to warming and salinification in the upper ocean. To the north of 50 °S, the deep-reaching warming and freshening that correspond to the ocean heat storage maximum are primarily set by the deepening of isopycnals. The large-scale patterns of isopycnal shoaling (deepening) at high (middle) latitudes are consistent with the overlying negative (positive) wind stress curl anomalies related to the poleward intensification of westerly winds, suggesting that the wind changes play an important role in the Southern Ocean heat redistribution under the ozone forcing.
... A potential agent is the semiannual oscillation (SAO) of the circumpolar trough (CPT). Earlier studies suggest that the SAO modulates the advance and retreat of the ice because it influences the location of the westerly and easterly surface winds which in turn promote or limit the spread of the ice (e.g., Enomoto & Ohmura, 1990;Stammerjohn et al., 2003). This is explored below. ...
... The volatility is considered to be due mainly to the dynamic effects of storms, ocean circulation (eddies), and wave-ice interaction at the ice edge. Stammerjohn et al. (2003) suggest that dynamics rather than thermodynamics initiate and dominate anomalies along the ice edge. The total observed volatility (Figure 7a) is lowest during the early stages of ice advance, large at SIE maximum and achieves a second, larger maximum later in the cycle, during the days of fastest sea ice retreat. ...
... We address now a factor that moderates the timing or phase of the annual cycle, the SAO. Although it has not been fully quantified, a number of studies suggest that the timing of advance and retreat of Antarctic sea ice is moderated by the SAO (Enomoto & Ohmura, 1990;Simmonds, 2003;Simmonds et al., 2005;Stammerjohn et al., 2003). An important characteristic of the southern hemisphere atmospheric circulation, the SAO is associated with more than 50% of the variability in SLP (Taschetto et al., 2007;van Loon & Rogers, 1984). ...
Understanding the variability of Antarctic sea ice is an ongoing challenge given the limitations of observed data. Coupled climate model simulations present the opportunity to examine this variability in Antarctic sea ice. Here, the daily sea ice extent simulated by the newly released National Center for Atmospheric Research (NCAR) Community Eart h System Model Version 2 (CESM2) for the historical period (1979–2014) is compared to the satellite‐observed daily sea ice extent for the same period. The comparisons are made using a newly developed suite of statistical metrics that estimates the variability of the sea ice extent on timescales ranging from the long‐term decadal to the short term, intraday scales. Assessed are the annual cycle, trend, day‐to‐day change, and the volatility, a new statistic that estimates the variability at the daily scale. Results show that the trend in observed daily sea ice is dominated by subdecadal variability with a weak positive linear trend superimposed. The CESM2 simulates comparable subdecadal variability but with a strong negative linear trend superimposed. The CESM2's annual cycle is similar in amplitude to the observed, key differences being the timing of ice advance and retreat. The sea ice begins its advance later, reaches its maximum later and begins retreat later in the CESM2. This is confirmed by the day‐to‐day change. Apparent in all of the sea ice regions, this behavior suggests the influence of the semiannual oscillation of the circumpolar trough. The volatility, which is associated with smaller scale dynamics such as storms, is smaller in the CESM2 than observed.
... Potential driving mechanisms underlying these changes include changes in surface temperature (Comiso et al., 2017), wind direction (Hobbs et al., 2016;Holland & Kwok, 2012;Massom et al., 2008;Mayewski et al., 2009;Stammerjohn et al., 2003;Turner et al., 2016), sea ice drift , precipitation (Liu & Curry, 2010), ice-ocean feedbacks (Goosse & Zunz, 2014), changes in the entrainment of warm deep water into the winter mixed layer (Zhang, 2007), and meltwater from the Antarctic ice sheet (Bronselaer et al., 2018). It is known that sea ice responds to many different interactive processes in the atmosphere and ocean (Hobbs et al., 2016). ...
... Several studies have focused on exploring the connections between the heterogeneous Antarctic sea ice trends and various climate , such as the SAM, the El Niño-Southern Oscillation (ENSO), and the IPO detailed below (Hobbs et al., 2016;Kwok et al., 2016;Lefebvre et al., 2004;Pezza et al., 2012;Stammerjohn et al., 2003Stammerjohn et al., , 2008, and on the role of seasonal feedbacks (Holland, 2014;Holland, Landrum, Raphael, et al., 2017). So far, no consensus has been reached on how climate modes affect the changes in Antarctic sea ice. ...
... Note that this pattern of slow growth and fast melt is observed in the averaged cycle for the whole Antarctic sea ice region, but significant regional variations do occur. For example, Stammerjohn et al. (2003) showed that in the western Antarctic Peninsula region, the sea ice advance season was generally either shorter than or equivalent to the period of sea ice retreat , which is opposite to the pattern for Antarctica as a whole. Although these regional variations have climatic, biological and biogeochemical consequences at the local scale, here we are interested in the annual cycle as a whole and in the fact that despite the substantial variation on wide-ranging time and space scales, the asymmetric annual cycle is consistent over the full measurement period. ...
Over the 40‐year satellite record, there has been a slight increasing trend in total annual mean Antarctic sea ice extent of approximately 1.5% per decade that is made up of the sum of significantly larger opposing regional trends. However, record increases in total Antarctic sea ice extent were observed during 2012–2014, followed by record lows (for the satellite era) through 2018. There is still no consensus on the main drivers of these trends, but it is generally believed that the atmosphere plays a significant role and that seasonal time scales and regional scale processes are important. Despite considerable yearly and regional variability, the mean seasonal cycle of growth and melt of Antarctic sea ice is strikingly consistent, with a slow growth but fast melt season. If we are to project trends in Antarctic sea ice and understand changes on longer time scales, we need to understand the mechanisms related to the seasonal cycle separately from those that drive variability. Twice‐yearly changes in the position and intensity of the zonal winds circling Antarctica are thought to drive the system by working with or against the evolving sea ice edge to slow the autumn advance and hasten the spring melt. Open water regions, created by divergence associated with the zonal winds, amplify the spring melt through increased warming of the upper ocean. Climate models fail to accurately reproduce mean Antarctic sea ice extent and overestimate its year‐to‐year variability, but they tend to capture the pattern and timing of the Antarctic seasonal cycle.
... The shelf processes outlined occur exclusively in the 'cold' sector of Antarctica (Figure 8.6), but it would be misleading to imply that sea ice does not play a major role in influencing the ocean in the 'warm' (Amundsen/Bellingshausen Sea) sector also. Indeed, it is one of the most significant factors in controlling ocean circulation and properties here, and feedbacks from the ocean to the ice are very important in determining the nature and behaviour of the ice cover in this region ( Stammerjohn et al., 2003;Venables & Meredith, 2014). ...
Sea ice around Antarctica plays a key role in determining the properties and circulation of the underlying Southern Ocean across a range of scales, whilst simultaneously numerous ocean processes impact profoundly on the temporally-evolving sea ice field. This chapter provides an overview of key aspects of this integrated system, including the nature and dynamics of the large-scale horizontal and overturning circulations of the Southern Ocean, the role of sea ice in producing various of the water masses that form here and which spread around the world, and ocean-ice interactions in the different climatic sectors of Antarctica. Improved capability for gathering ocean data are required in order to better understand the interplay of ocean and ice, and to better predict the consequences for regional and global climate; the status and future of the observing system required to achieve this are outlined.
... The seasonal strengthening and poleward intensification of the CPT has a distinct effect on the timing of the annual ice edge advance and retreat (Enomoto & Ohmura, 1990;Watkins & Simmonds, 1999;van den Broeke, 2000;Stammerjohn et al., 2003;Yuan & Li, 2008). The low-pressure minimum defining the CPT marks the boundary between westerlies to the north and easterlies to the south. ...
Every year Antarctic sea ice undergoes a six-fold change in ice-covered area; it is one of the largest seasonal signals on earth. It is however highly variable and frequently exposed to strong storms, high winds and waves. These factors affect Antarctic sea ice growth and melt processes, thickness evolution and drift and impart high regional and seasonal variability. Over the past four decades there has been a modest increase in spatially averaged Antarctic sea ice extent, but this hides very large but opposing regional sea ice trends. In the highest trending regions, rates of change are comparable to those observed in the Arctic, but elsewhere around Antarctica, sea ice trends lie within the range of natural variability. Local differences in air-sea-ice interactions and sensitivity to large-scale climate variability create a complex picture in terms of attribution. Historical sea ice observations lend perspective, suggesting different behavior in the recent past.
... Therefore, the timing of the development and retreat of sea ice are considered as important factors in the temporal variability of phytoplankton communities in the AP (Arrigo et al., 1999;Garibotti et al., 2003Garibotti et al., , 2005Moline and Prézelin, 1996). Although the dynamics of sea ice are influenced by winds (Stammerjohn et al., 2003, and references therein), here we related these dynamics only with temperature. In our study, SSC, SST and sea ice area (on a monthly basis) were best correlated considering a zero lag time, according to the cross-correlation analysis (see Table 5). ...
Spatial variability and interannual variability of phytoplankton biomass, estimated as chlorophyll-a (Chl-a) concentration and taxonomic groups, were analyzed in relation to environmental conditions in the Bransfield Strait (BS). This study is based upon both in situ data, during the austral summer. A thermohaline front was predominately observed between the colder and saltier waters under the influence of transitional water with Weddell Sea influence (TWW) in the southeastern BS, and the fresher and warmer waters associated with the presence of transitional water with Bellingshausen Sea influence (TBW) in the northwestern BS. Canonical correspondence analysis showed that the dominance of microplanktonic diatoms was associated with higher Chl-a within shallow upper mixed layers, with relatively strong pycnocline in the TBW, particularly close to the South Shetland Islands (SSI). Conversely, the TWW was primarily characterized by lower Chl-a within deeper mixed layers or a well-mixed water column and dominated by nanoplanktonic flagellates (including haptophytes and cryptophytes). Spatial variability based on both in situ and satellite data suggests that the Bransfield Strait acts as a typical Seasonal Ice Zone (SIZ) and the phytoplankton community there is governed by a combination of processes acting synergistically: the sea ice retreat, allowing for a penetration of light into the water column, and a relatively shallow upper mixed layer with strong pycnocline, primarily in the TBW, retaining organisms near the surface when light conditions are adequate. Interannual variability in Chl-a and species composition indicate an alternation between diatom-dominated and flagellate-dominated assemblages. These shifts are potentially related to the different stages of phytoplankton succession, as a result of varying water column physical features, principally influenced by the dynamic occupation of the TBW and TWW, that appear to modulate phytoplankton dynamics within the BS.
... Strong northerly winds drive the ice edge southward, delaying ice edge advance in autumn and accelerating its retreat in spring, often synoptically with each passing storm (Stammerjohn et al., 2003;Massom et al., 2008). Increased solar ocean warming in summer (due to earlier and longer ice-free conditions) is also contributing to the sea ice changes, acting as a positive feedback to enhance and sustain the rate of warming and sea ice retreat (Meredith and King, 2005;Stammerjohn et al., 2011). ...
The extent, duration, and seasonality of sea ice and glacial discharge strongly influence Antarctic marine ecosystems. Most organisms' life cycles in this region are attuned to ice seasonality. The annual retreat and melting of sea ice in the austral spring stratifies the upper ocean, triggering large phytoplankton blooms. The magnitude of the blooms is proportional to the winter extent of ice cover, which can act as a barrier to wind mixing. Antarctic krill, one of the most abundant metazoan populations on Earth, consume phytoplankton blooms dominated by large diatoms. Krill, in turn, support a large biomass of predators, including penguins, seals, and whales. Human activity has altered even these remote ecosystems. The western Antarctic Peninsula region has warmed by 7°C over the past 50 years, and sea ice duration has declined by almost 100 days since 1978, causing a decrease in phytoplankton productivity in the northern peninsula region. Besides climate change, Antarctic marine systems have been greatly altered by harvesting of the great whales and now krill. It is unclear to what extent the ecosystems we observe today differ from the pristine state.
