Comparative Systematic Analysis of Milankovitch Cycles to Identify Variations of Glaciers and Interglacial Periods of Late Pleistocene in South Asia

Abstract

Variations in the first Euler angle known as Earth precession phenomenon which is described as a change in the Earth's orbit; found to have strong impact on the climate of Earth. These observations of climate changes were connected with the behavior of the global ice sheets, including their advancing and retreating movements which have been recorded. In fact, Earth's climate depends essentially on the cycle of glaciers' growth and reduction. The alternative glacial periods and the interglacial periods coincide with the variations in Earth's orbit known as "Milankovitch cycles", which affect the insolation, and the sunlight exposure of different regions of the world and thus ultimately the behavior of ice formation. This paper aims to document the variations of the Earth's axis orientation and to discuss how these changes have affected to the sea-level fluctuation of the South Asian Region during late Pleistocene. Experiment methodology consists of compelling a standardized dataset of the sea-level index (Data SET 01-Radiocarbon Journal, Katupotha. J, Data SET 02-SEAMIS database and selected 35 number of carbon dating values recorded and published in the literature of the South Asian Region) and then compare it with the data of Milankovitch Cycles. The discussed results show that the sea-level variations occurred mainly between 12,500 ± 1,500 YBP to 11,000± 1,500 YBP, indicating that 25m ± 5m recorded to be the lower sea level documented than the current sea level found around the South Asian region. This has been resulted by a quick glacier transition that happened in the Late Pleistocene.

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Comparative Systematic Analysis of Milankovitch Cycles to
Identify Variations of Glaciers and Interglacial Periods of
Late Pleistocene in South Asia
Aravinda Ravibhanu1, Jinadasa Katupotha2, Majda Aouititen3
1,3 Department of Research & Innovation - South Asian Astrobiology & Earth Sciences Research Unit: Eco Astronomy Sri Lanka.
2 Department of Geography University of Sri Jayewardenepura, Sri Lanka.
3Beijing Forestry University School of Ecology and Nature Conservation, Beijing, China.
aravinda@ecoastronomy.edu.lk
Abstract
Variations in the first Euler angle known as Earth precession phenomenon which is
described as a change in the Earth’s orbit; found to have strong impact on the climate of
Earth. These observations of climate changes were connected with the behavior of the
global ice sheets, including their advancing and retreating movements which have been
recorded. In fact, Earth’s climate depends essentially on the cycle of glaciers' growth and
reduction. The alternative glacial periods and the interglacial periods coincide with the
variations in Earth’s orbit known as “Milankovitch cycles”, which affect the insolation,
and the sunlight exposure of different regions of the world and thus ultimately the behavior
of ice formation. This paper aims to document the variations of the Earth’s axis
orientation and to discuss how these changes have affected to the sea-level fluctuation of
the South Asian Region during late Pleistocene. Experiment methodology consists of
compelling a standardized dataset of the sea-level index (Data SET 01-Radiocarbon
Journal, Katupotha. J, Data SET 02- SEAMIS database and selected 35 number of carbon
dating values recorded and published in the literature of the South Asian Region) and then
compare it with the data of Milankovitch Cycles. The discussed results show that the sea-
level variations occurred mainly between 12,500 ± 1,500 YBP to 11,000± 1,500 YBP,
indicating that 25m ± 5m recorded to be the lower sea level documented than the current
sea level found around the South Asian region. This has been resulted by a quick glacier
transition that happened in the Late Pleistocene.
Keywords: Milankovitch cycles, Sri Lanka, Sea Level, Carbon dating, Late Pleistocene.

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Introduction
The glacial-interglacial cycles over the late Pleistocene provide a strong framework
for understanding the evolution of the climate events over the Holocene. The main
objective is to study factors that effecting to changes of interglacial to glaciers
environment and glaciers to the interglacial environment mainly focusing on
Milankovitch cycles and sea-level fluctuation. However, ‘Milankovitch cycles’ are
insufficient to explain the full range of late “Quaternary climate change, which is also
required to compare with the influence of the greenhouse gas and the
albedo variations, but they are a primary forcing that must be accounted
(Milankovitch,1930). ‘Milankovitch cycles’ are classically divided into three
components as the earth’s precession, the earth’s obliquity, and the earth’s
eccentricity cycles. These cycles modulate the solar insolation or its geographic
distribution. Orbital and precession variations are also likely to be a generic feature
of the other planets, with significant implications for the fate of
planetary atmospheres and tend to help us understand the potential of habitability on
the other planets. Especially, considering the partial harbour life environment of
quaternary habitats in Sabaragamuwa basin observed during the late Pleistocene in
Sri Lanka (Sumanarathna,2017). In fact, many proxy's data show that Earth’s climate
has under process the glacial-interglacial cycle with semiregular periodicity, with
phases strongly linked to orbital variations (Hays et al., 1976; Huybers and Curry,
2006; Imbrie, 1984; Imbrie et al., 1992; Lisiecki and Raymo, 2005). For the past
~0.80 Ma, the main periodicity has been described as the eccentricity (~100 kyr)
embedded with the precession (~21 kyr) and the obliquity (~40 kyr) signals (El Kibbi
et al., 2001). Before ~0.8 Ma, the main signal was obliquity with weak eccentricity
and precession signals (Imbrie, 1984; Lisiecki and Raymo, 2005), and this shift has
been happened in the late to mid - Pleistocene transition that leads to amplify the
initial cooling (Fig. 1).
Due to the predominance of northern hemispheric glaciers, the northern hemispheric
insolation is usually the assumed driver of the glacial-interglacial cycle
(Milankovitch, 1930). Having the strong signal of eccentricity during the past 0.8

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Myr since the present has been puzzled because the effect of eccentricity on seasonal
insolation is small (Imbrie et al., 1992), although eccentricity modulates precession
(Lisiecki, 2010). However, it has been proposed that the 100 kyr cycle may be a
modulation of the obliquity signal because the integrated seasonal insolation at a
given location does not change with precession (Huybers, 2003, 2006). While
numerous studies link paleo proxies to insolation forcing, there is yet no broadly
accepted explanation for how ice ages started as well as why they follow a 100 kyr
cycle, and why the pace of the glacial cycle changes in Quaternary.
Materials & Methodology
The methodology that has been applied for this study was to compile standardized
datasets (https://github.com/Alerovere/SEAMIS) of the sea-level index and limiting
points which meet the criteria recently summarized. It includes Data SET 01-Radio
Carbon Journal, Katupotha. J (Ref: 10-14) carbon dating values in the west coast of
Sri Lanka. Data SET 02- SEAMIS database, including another random carbon dating
from India, Singapore, Malaysia, Maldives, Thailand, Vietnam, and Cambodia (Ref
:8). In this paper, these geochronological data have been compared with the data of
Milankovitch cycles.

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Results
Figure 1. (A) Variables of proxies in the last 0.8Ma and (B) Graph depicting orbital variations, solar
energy changes, and resulting glacial cycles, as a consequence of Milankovitch cycles, demonstrating
solar and orbital forcing of climate on 800kyr intervals; Adapted from Quinn et al. (1991) and Lisiecki
and Raymo (2005). (C) Temperature Variations (blue), CO 2 (green), and Dust content (red) in an ice
core dated 12kyr; Willy and Walter (2012). (D) and (E) Axial precession’s stages via one cycle
representing the Sun light exposure into the South Asian region; (Buis., 2020). (F) The Earth’s axis
angle of rotation is tilted as it travels around the Sun which is known as obliquity; (Buis., 2020).

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Figure 2: (H) & (I)The shape of Earth’s orbit, known as eccentricity, and its effectivity on surface
temperature variation (Buis., 2020).
Figure 3: Map representing region and counties of the sea-level index and limiting points meet the
criteria recently summarized (https://github.com/Alerovere/SEAMIS).

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Table 1: Details on the Earth model parameters and different mantle viscosity profiles employed to
simulate glacial isostatic adjustment combined with the Ice model ICE-5G in the areas of
interest(https://github.com/Alerovere/SEAMIS). Model short names refer to the different model curves
in graph A and B
Figure 4: Graph A (Left) Average values of relative sea-level data index
(https://github.com/Alerovere/SEAMIS) relevant to observed countries, as mentioned in fig.3. Graph B
(Right) Average values of relative sea-level data index; Katupotha. J (Ref: 10-14) Sri Lanka (Mann et
al, 2019 and Sumanarathna et al, 2021)

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Discussion
Interpreting “Fig.1-B” the grey represents the peaks of global variations in
temperature that identify interglacial periods of relatively warm climate typical
recorded over the past thousands’ years; the ice periods are represented by the valleys
between peaks of grey areas; the three curves on the top are the Milankovitch cycles
of Earth's orbital changes caused by the precession, the obliquity of polar axes, as
well as the eccentricity of the orbit these cycles where changes to orbital eccentricity
occur at 400,000 and 100,000yr intervals; the variations in axial tilt occur at 40,000yr
intervals, and the changes in the axial precession occur at 25,000yrs (Wanner et al.,
2008; Bennet, 1990; Imbrie and Imbrie, 1979, Dawson, 1992; Raymo and
Nisancioglu, 2003); in addition, the fourth curve is the changes documented for the
solar forcing; finally, the bottom curve is the temperature changes which get impacted
by these other influences. The orbital variations, solar energy changes and resulting
glacial cycles, as a consequence of Milankovitch cycles, demonstrating solar and
orbital forcing of climate on 100kyr intervals (Fig.1-B) shows the effects of
Precession, Obliquity, Eccentricity, and Solar Forcing which refers to the quantity of
solar radiation that reaches the Earth’s atmosphere as a result of both solar and
astronomical forcing (Berger et al., 2013), which includes axial orientation and
positioning relative to the Sun on Glacial Interglacial cycles.
Earth’s orbit wobbles shown in “Fig.1-D, E,” called Precession cycles, result in a
change of the amount of sunlight at middle latitudes by up to 25% and cause the
climate to oscillate. Using deep-sea sediment cores found that Milankovitch
cycles correspond with periods of major climate change over the past 450,000 years,
with Ice Ages occurring when Earth was undergoing different stages of orbital
variation (Buis., 2020). When Earth’s orbit made northern summers warmer than
average, huge pieces of ice were melted through North America, Europe, and Asia;
but then when the orbit cooled northern summers, those ice sheets started to advance
again. In fact, oceans dissolve less carbon dioxide when it reaches low temperatures,
which will lead to a reduction in the atmospheric carbon dioxide levels (Fig.1-C), and
this will fall in concert with these orbital wobbles, multiplying their impacts. Also, as

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mentioned in Fig .1-C, the amount of dusty particle has been increased around 10.5ka
to 12.5 ka. It could be a result of a meteorite impact more specifically; it could take
place during the younger dryas condition.
After measuring (Fig. 2 and 3 ) the centricity of how circular a curve is with e=0
describing a circular orbit, 0 < e < 1 is an elliptic orbit, e=1 describing a parabolic
trajectory, and e > 1 is for hyperbolic trajectory; taking in consideration the timescale
of Earth’s eccentricity variation during the 100,000-year cycle as it is represented in
“Fig. 2” the orbital eccentricity characterizes in this case how circular e=0.0034 (Fig.
2-H) or slightly elliptical-shaped e=0.058 (Fig. 2-I) our planet Earth orbit around the
Sun. Moreover, this orbital eccentricity could explain and even be considered to have
directly impacted the climate change recorded in the Asian region. Due to the
variations in the quantity of the solar energy received on Earth, as the northern
hemisphere winters become relatively longer and the summers become shorter; which
will have effects in the sea-level index represented in “Fig. 3”. This case observed in
the glacial and the interglacial cycles that have driven immense variation in the mean
sea level globally (Lambeck and Chappell 2001). These cycles are controlled by
eccentricity, which brings us to assume that Milankovitch orbital cycles are the reason
for the Earth’s glacial and interglacial cycles and the first-order climatic changes,
which have caused sea-level oscillations that were important during the Quaternary
(Hays, Imbrie & Shackleton, 1976; Muller & MacDonald, 1997; Wunsch, 2004).
(Table. 1 and fig. 4) Graph A (Left) represent the average values of relative sea-level
index relevant to observed countries and Graph B (Right) of “fig.4” created based on
data mentioned in “table. 1” indicate the average values of relative sea-level data
index in Sri Lanka, after analyzing the curves on both graphs it is obvious that during
years the average sea-level has been changed, the driving force behind these large-
scale changes is ‘orbital forcing’. Considering the past period globally speaking so
far in the previous 18,000 years ago, the Earth's temperature has risen approximately
9 °F that results in a risen of sea level by 300 feet. 18,000 years ago, the climate
begins to warm up (Smith et al., 2013), then 15,000 years ago advance of glaciers
halts and sea levels begin to rise, followed by the ice age megafauna that goes extinct

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10,000 years ago, still, 8,000 years ago Bering Strait land bridge becomes drowned,
stopping the migration of men and animals (Sumanarathna,2017). Collectively,
variations in Earth's orbit which are known as eccentricity, obliquity, and precession,
can either reinforce signatures of cooling or warming, much more they can counteract
each other and produce less severe or ameliorated climate change.
Conclusion
The above results show that the sea-level variations occurred between 12,500 ± 1,500
YBP to 11,000± 1,500 YBP, indicating that 25m ± 5m recorded to be the lower sea-level
documented compared to the current sea-level found around the South Asian region
(https://github.com/Alerovere/SEAMIS). Considering the fundamental data of
precession, obliquity, and eccentricity, including the glacier cycles data, represent the
gradual temperature drop between 13.5ka to 10.5ka. When Earth's orbit becomes
more eccentric, the semi-minor axis shortens. That will result in an increase of the
seasonal changes magnitude. The sea ice growth is concluded to be a rapid—ice
increased in the South Asian ocean affecting the precession stage with long-lasting
low sunlight and albedo. Though the situation of planet Earth indicate that we are
approaching again the minimum amount of sunlight, in other words, we are going
towards a new ice age within no less than 14,000 years (Fig. 5). More further studies
based on statistical data of those selected countries are needed, which will give us a
clear understanding on what has happened.
Figure 5: A simulation model for average sea-level fluctuations in South Asia, around 12,000 yr. BP-
12,800yr BP. (Left: Glacier model and Right: Warm and inter glacier model)

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Acknowledgement
This work was supported by the South Asian Astrobiology Earth Sciences Research
Unit of Eco Astronomy Sri Lanka as a part of the project: Harbor Life in South Asia
_2019. We address our gratitude to Sonam Wangchuk from the Himalayan Institute
of Alternatives (HIAL).
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INDICATE ... Retrieved February 02, 2021, from
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