Indian Ocean Sector Research Articles

The mechanism linking the variability of the Antarctic sea ice extent in the Indian Ocean sector to Indian summer monsoon rainfall.

The study investigates the mechanism of teleconnection between the variability of sea ice extent (SIE) in the Indian Ocean sector of the Southern Ocean and the variability of Indian summer monsoon rainfall. We utilized reanalysis, satellite, in-situ observation data, and model output from the coupled model intercomparison project phase 5 (CMIP5) from 1979 to 2013. The empirical orthogonal function (EOF) and correlation analysis show that the first and third modes of principal component (PC1 and PC3) of SIE in the Indian Ocean sector during April–May–June (AMJ) are significantly correlated with the second mode of principal component (PC2) of Indian summer monsoon rainfall. The reanalysis data revealed that the changes in the SIE in the Indian Ocean sector excite meridional wave train responses along the Indian Ocean for both principal component modes. Positive (negative) SIE anomalies based on first and third EOFs (EOF1 and EOF3), contribute to the strengthening (weakening) of the Polar, Ferrel, and Hadley cells, inducing stronger (weaker) convective activity over the Indian latitudes. The stronger (weaker) convective activity over the Indian region leads to more (less) rainfall over the region during high (low) ice phase years. Furthermore, a stronger (weaker) polar jet during the high (low) ice phase is also noted. The selected CMIP5 models captured certain atmospheric teleconnection features found in the reanalysis. During AMJ, the SIE simulated by the NorESM1-M model was significantly positively correlated with Indian summer monsoon rainfall, whereas the IPSL-CM54-LR model showed a negative correlation.

Recent changes and distribution of the newly-formed Cape Darnley Bottom Water, East Antarctica

Hydrographic top-to-bottom CTDs and profiling float profiles were collected during 2003–2020 periods in the south-west Indian Ocean sector of the Antarctic margin. Those calibrated dissolved oxygen, temperature and salinity records were used to document the distribution, pathway and changes of the newly-formed Cape Darnley Bottom Water (CDBW). We found that the newly-formed CDBW, with high fractions (50–90%) in the bottom 300 m, primarily appeared on the continental slope (64.5°-70°E) and the abyssal ocean (57°-64.5°E) in the eastern Cooperation Sea. Those distributions of CDBW fractions suggested a pathway originating from the Cape Darnley Polynya (CDP) and descending down Wild and Daly Canyons, and finally accumulating in the northwest abyssal ocean. The newly-formed CDBW presented decadal changes in potential temperature, salinity, dissolved oxygen, and neutral density between 2003-2006 and 2013–2020. It showed significant cooling (∼0.098 °C/decade), freshening (∼0.013/decade), increasing dissolved oxygen (∼11.8 μmol/kg/decade) rates on the continental slope just off CDP, while warming (0.018–0.038 °C/decade), freshening (0.0044–0.0055/decade), decreasing density (0.009–0.014 kg/m3/decade) and increasing dissolved oxygen (4–12 μmol/kg/decade) in the Daly Canyon. The most likely explanation of those high change rates is the enhanced CDBW formation caused by increased cascading Dense Shelf Water (DSW) plumes in Daly Canyon, and subsequently enhanced entrainment of warmer mid-depth Modified Circumpolar Deep Water (MCDW). In the northwest abyssal plain, the potential temperature and dissolved oxygen show little change while the freshening and more buoyant signals remain considerable, which might be influenced by the changes of AABWs from different sources. Finally, we relate the recent changes of newly-formed CDBW to the Sea Ice Production (SIP) change in the CDP. The SIP in the CDP shows significant increasing trends (0.52 m/decade) during 2002–2020. It increased by 12.5% during this period, which indicates an increased formation of regional DSW driven by the sea-ice formation and associated brine rejection, thus increasing formation of CDBW. Those processes were likely responsible for the decadal changes of the recently-formed CDBW.

Sea ice variability and trends in the Indian Ocean sector of Antarctica: Interaction with ENSO and SAM

Antarctic sea ice variability is primarily associated with ocean-atmospheric forcing driven by anomalous conditions over the tropical regions of the Pacific and Indian Oceans. The ice-ocean-atmosphere dynamics in the Indian Ocean Sector (IOS) of Antarctica have been studied using monthly satellite and reanalysis observations over four decades (1979–2019). In this study, we revealed that the annual sea ice extent (SIE) in the IOS increases at a rate of 0.7 ± 0.9% decade−1, with a maximum increase in austral summer (5.9 ± 3.7% decade−1). The wavelet approach was used to determine the variability in IOS sea ice caused by the El Niño/Southern Oscillation (ENSO) and southern annular mode (SAM). The SIE has a significant association with both indices during the summer and autumn. In comparison to ENSO, the sea ice variability associated with SAM is typically seasonal in nature and lacks distinct patterns. The wavelet coherence analysis revealed a relatively weak relationship between ENSO and SAM but a highly significant coherence between climatic indices and SIE. We observed that sea ice in the IOS is influenced significantly by climatic oscillations during their negative SAM/El Niño or positive SAM/La Niña phases. Furthermore, the study demonstrated a substantial impact of climatic disturbances in determining the sea ice variability in the IOS.

An Unprecedented Record Low Antarctic Sea-ice Extent during Austral Summer 2022

Seasonal minimum Antarctic sea ice extent (SIE) in 2022 hit a new record low since recordkeeping began in 1978 of 1.9 million km2 on 25 February, 0.17 million km2 lower than the previous record low set in 2017. Significant negative anomalies in the Bellingshausen/Amundsen Seas, the Weddell Sea, and the western Indian Ocean sector led to the new record minimum. The sea ice budget analysis presented here shows that thermodynamic processes dominate sea ice loss in summer through enhanced poleward heat transport and albedo-temperature feedback. In spring, both dynamic and thermodynamic processes contribute to negative sea ice anomalies. Specifically, dynamic ice loss dominates in the Amundsen Sea as evidenced by sea ice thickness (SIT) change, while positive surface heat fluxes contribute most to sea ice melt in the Weddell Sea.

Atmospheric drivers of a winter-to-spring Lagrangian sea-ice drift in the Eastern Antarctic marginal ice zone

AbstractSea-ice drift in the Antarctic marginal ice zone (MIZ) is discussed using data from a 4-month-long drift of a buoy deployed on a pancake ice floe during the winter sea-ice expansion. We demonstrate increased meandering and drift speeds, and changes in the dynamical regimes of the absolute dispersion during cyclone activity, together with high correlations between drift velocities and wind from atmospheric reanalyses. This indicates a dominant physical control of wind forcing on ice drift and the persistence of free-drift conditions. These conditions occurred despite the buoy remaining largely in >80% ice concentrations and at distances >200 km from the estimated ice edge. The drift is additionally characterised by a strong inertial signature at 13.47 h, which appears initiated by passing cyclones. A wavelet analysis of the buoy's velocity confirms that the momentum transfer from winds at the multi-day frequencies is due to atmospheric forcing, while the initiation of inertial oscillations of sea ice has been identified as the secondary effect. Propagating storm-generated waves may initiate inertial oscillations by increasing the mobility of floes and enhance the drag of the inertial current. This analysis indicates that the Antarctic MIZ in the Indian Ocean sector remains much wider and mobile, during austral winter-to-spring, than defined by sea-ice concentration.

Copepod assemblages in the water column and drifting sea-ice floes in the ice-edge region in the Indian Ocean sector of the Southern Ocean during the austral summer

Copepod assemblages in the water column and drifting sea-ice floes in the ice-edge region in the Indian Ocean sector of the Southern Ocean during the austral summer

High-frequency noise and depth error associated with the XCTD/XBT profiles in the Indian Ocean sector of Southern Ocean and southwestern tropical Indian Ocean

High-frequency noise and depth error associated with the XCTD/XBT profiles in the Indian Ocean sector of Southern Ocean and southwestern tropical Indian Ocean

Distributions of virio- and picoplankton and their relationships with ice-melting and upwelling in the Indian Ocean sector of East Antarctica

Ice melting in the Antarctic summer and upwelling of the Circumpolar Deep Water (CDW) near the Antarctic continent have been suggested to regulate the distributions of microbial communities. However, an understanding of these relationships in the Indian Ocean sector of East Antarctica is lacking. We report on the distribution and relationships of virio- and picoplankton at 77 stations (including 29 stations throughout the entire water column and 48 stations from the epipelagic zone) from 35° to 78°E and 62° to 70°S, covering the Cosmonaut Sea, Cooperation Sea and Prydz Bay. The epipelagic stations were grouped into four clusters based on the virio- and picoplankton composition and abundance. Clusters three and four, which corresponded with areas of upwelling and ice retreat, had high abundances of autotrophic picoeukaryotes; this resulted in subsequent high abundances of heterotrophic prokaryotes and virioplankton. Cluster one and two stations correspond with a high nutrient, low chlorophyll (HNLC) area, where the abundances of autotrophic and heterotrophic picoplankton are low. Viruses were significantly correlated with heterotrophic prokaryotes in the ice-covered areas but more strongly correlated with autotrophic picoeukaryotes in areas associated with ice-edge blooms. Throughout the water column in the Cooperation Sea, nutrient supply from the upwelling of the CDW induced an increased abundance of heterotrophic prokaryotes, particularly in the meso- and bathypelagic zones of stations in the northern part of the area. High viral abundances were detected in the meso- and bathypelagic zones of stations with high abundances of virio- and picoplankton in the epipelagic zone. This study shows that the summer distribution of virio- and picoplankton in the Indian Ocean sector of East Antarctica was mainly controlled by ice-melting and upwelling of the CDW.

Spatial hydrochemical structure in surface waters of the Southern ocean between Africa and Antarctica

Some hydrochemical characteristics and, first of all, the main nutrients (phosphorus, nitrogen, silicon) can be used as markers for distinguishing different types of water masses and positions of the main fronts of the Southern Ocean. The seasonal and interannual variability of these characteristics also reflects the character of biological processes in the surface layer of the ocean, which is important for assessing biological productivity. The aim of this study was to analyze the main features of the spatial distribution of hydrochemical characteristics in the surface layer in the Atlantic and Indian Ocean sectors of the Southern Ocean between the Subantarctic Front and the shores of Antarctica and assess their seasonal (spring–autumn) and interannual variability for the observation period from 2008 to 2020. We describe the surface nutrient concentrations between Africa and Antarctica along the transects that cross the Subantarctic Front (SAF) in the north, the Polar Frontal Zone (PFS), Polar Front (PF) and Antarctic Zone water in the south. The findings revealed an increase in dissolved oxygen and nutrients towards the south. Nitrates changed values within the SAF from 15 μM to 24 μM, whereas values from 1.2 μM to 1.7 μM were observed for phosphates. Silicate increased considerably within the Polar Front, from 6.6 μM to 20.8 μM. An analysis was carried out of the seasonal and interannual variability of the hydrochemical conditions in the surface layer of the Southern Ocean. The interannual variability of the nutrients was determined by the spatial variability of the main fronts of the Antarctic Circumpolar Current (ACC) and the intensity of the largescale Weddell Gyre (WG). Since 2017, there has been an increase in the meridional transfer of waters: in the Antarctic Summer 2017–2018, there was a spreading of high-nutrient WG waters toward the north, and in the Summer 2019–2020, the low-nutrient waters anomaly was transferred far to the south (up to 60°S).According to the data obtained, the seasonal dynamics of the nutrients in the surface layer of the Southern Ocean was rather weakly expressed. An exception is the high-latitude waters of the Cooperation and Davis Seas, where maximum seasonal variability of the hydrochemical characteristics was observed. The highest rate of nutrient consumption was observed in the coastal area of the Cooperation Sea near the fast ice edge from mid–December to early January and reached 3.2 μM per day for silicate, 1.8 μM per day for nitrates, and 0.12 μM per day for mineral phosphorus. The results of the long-term monitoring of the hydrochemical conditions in the Cooperation Sea made it possible to distinguish conditionally “warm” years with early vegetation (at the end of December) and intensive consumption of nutrients by phytoplankton, and “cold” years, when the formation of high-latitude “oases” in December–January was not observed.

Sea Ice Variability and Trends in the Western Indian Ocean Sector of Antarctica During the Past Two Centuries and Its Response to Climatic Modes

AbstractAntarctic sea ice is a critical component of the ocean‐climate system. Sea ice concentration (SIC) records of various oceanic sectors of Antarctica available since 1979 reveal dramatic changes in recent years; however, there is no consensus yet on drivers of sea ice variability, changes and their future projections. The lack of long‐term SIC records has impeded the quantification of sea ice variability, trends and various forcing factors and mechanisms. Here, we present a long‐term SIC record (1809−1993 CE) for the Western Indian Ocean Sector (WIOS) of Antarctica derived from a new ice core oxygen isotope (δ18O) record together with three available records from Dronning Maud Land (DML), East Antarctica. This long‐term SIC record at annual resolution reveals a significant decline during 1830–1884 CE with a rate of 0.58% ± 0.12% decade−1 followed by moderate increase during 1927–1993 CE with a rate of 0.24% ± 0.11% decade−1. Current satellite‐derived SIC records reveal an increase of 2.59 ± 0.86% decade−1 during 1994–2014 CE, which is unprecedented over the last two centuries as determined by the ice core‐derived SIC record. The satellite and ice core combined SIC record (1809−2019 CE) also reveals a significant increase in interannual variability at El Niño Southern Oscillation band and decadal variability at 16–32 years band in the last few decades. Our investigation suggests that wind‐driven sea‐ice dynamics associated with switching phases of Southern Annular Mode and remote teleconnections of Pacific oscillations largely control the interannual to decadal sea ice variability in this region.

Hemispheric Asymmetry in Future Wave Power Changes: Seasonality and Physical Mechanisms

AbstractThis study inspects the global changes in ocean wave power (WP) by the end of the 21st century, relative to the 1979–2005 period, focusing on seasonality and physical mechanisms. The multimodel ocean wave simulations from WAVEWATCH‐III, forced with surface winds simulated by seven different CMIP5 global climate models, are particularly examined. These models robustly show a hemispheric asymmetry in WP changes, that is, a decrease in the Northern Hemisphere but an increase in the tropics and Southern Hemisphere, with large seasonal and regional variations. Individual terms of differential WP, which include wave height and wave period changes, are analyzed to isolate the role of each process. Although wave height changes dominate the overall WP changes, wave period changes also play a comparable role in the Southern Hemisphere extratropics especially in the Indian Ocean sector during austral winter (12%). Wave period increase is strikingly higher in austral winter than summer, resembling swell height changes in the Southern Ocean. Intermodel correlation and composite analyses further indicate that the WP increase in the Southern Hemisphere is closely associated with positive Southern Annular Mode (SAM) trend. On the other hand, the WP decrease in the Northern Hemisphere is robustly related with weakened meridional surface temperature gradient during winter, a consequence of Arctic amplification. As a result, models with higher positive SAM trend and larger Arctic warming project stronger hemispheric asymmetries in WP changes.

Redescription of two rare, deep-sea species of hyperiidean amphipod, Lanceola loveni antarctica Vinogradov, 1962 and L. sphaerica Vinogradov, 1970 (Crustacea: Amphipoda: Hyperiidea: Lanceolidae)

Lanceola loveni antarctica and L. sphaerica are rare deep-sea species known from very few specimens. Until recently (Zeidler 2019) L. loveni antarctica was known only from the types, seven specimens (727 mm), from the Indian Ocean Sector of the Antarctic (Vinogradov 1962). Similarly, L. sphaerica, originally described as a variety of L. clausi (Vinogradov, 1957), based on two damaged specimens, a female (8.0 mm) and a male (9 mm), from the Kurile-Kamchatka region of the NW Pacific, later elevated to full species status by Vinogradov (1970) upon the discovery of a well-preserved male (5 mm) from the same general region, was until then known only from these three specimens. The recent discovery of several specimens of both species in the USNM (Zeidler 2019) has now made it possible to provide a more detailed redescription of these rare species, including some new distribution records.

Biogenic aerosol in central East Antarctic Plateau as a proxy for the ocean-atmosphere interaction in the Southern Ocean

Ten years of data of biogenic aerosol (methane sulfonic acid, MSA, and non-sea salt sulfate, nssSO42−) collected at Concordia Station in the East Antarctic plateau (75° 06′ S, 123° 20′ E) are interpreted as a function of the Southern Annular Mode (SAM), Chlorophyll-a concentration (Chl-a; a proxy for phytoplankton biomass), sea ice extent and area. It is possible to draw three different scenarios that link these parameters in early, middle, and late summer. In early summer, the biogenic aerosol is significantly correlated to sea ice retreats through the phytoplankton biomass increases. Chl-a shows a significant correlation with nssSO42− in the finest fraction (< 1 μm). In contrast, only Chl-a in West Pacific and Indian Ocean sectors correlates with MSA in the coarse fraction. The transport routes towards the inner Antarctic plateau and aerosol formation processes could explain the different correlation patterns of the two compounds both resulting from the DMS oxidation. In mid-summer, Chl-a concentrations are at the maximum and are not related to sea ice melting. Due to the complexity of transport processes of air masses towards the Antarctic plateau, the MSA concentrations are low and not related to Chl-a concentration. In late summer, MSA and nssSO42− present the highest concentrations in their submicrometric aerosol fraction, and both are significantly correlated with Chl-a but not with the sea ice. In early and mid-summer, the enhanced efficiency of transport processes from all the surrounding oceanic sectors with air masses traveling at low elevation can explain the highest concentrations of nssSO42− and especially MSA. Finally, considering the entire time series, MSA shows significant year-to-year variability. This variability is significantly correlated with SAM but with a different time lag in early (0-month lag) and late summer (4-months lag). This correlation likely occurs through the effect of the SAM on phytoplankton blooms.

Deep sea without limitsfour new closely related species of Emertonia Wilson, 1932 (Copepoda: Harpacticoida: Paramesochridae) show characters with a world-wide distribution.

The large-scale dispersal of deep-sea harpacticoid copepods is an increasing focus for ecological studies. A fundamental prerequisite for monitoring and explaining their geographical distribution is precise descriptions of their morphology. Four new, closely related species of the family Paramesochridae (Copepoda, Harpacticoida) were found in the deep sea of the Pacific (San Diego Trough and off Chile), the Atlantic Ocean (Porcupine Abyssal Plain and Angola Basin), and the Atlantic and Indian Ocean sectors of the Southern Ocean (Weddell Sea and off Crozet Island). The discovery of Emertonia berndi sp. nov., E. hessleri sp. nov., E. ilse sp. nov., and E. serrata sp. nov. increases the number of known deep-sea species in this genus to ten. The new species are placed in Emertonia Wilson, 1932 because of their one-segmented endopods on the second and third swimming legs. The presence of a two-segmented endopod on the fourth swimming leg allocates them to the andeep-group within this genus. The four species can be distinguished from their congeners by the strongly serrated spines on the exopods of their swimming legs and an outwardly directed flexible seta on the exopod of the fifth leg. It is conveivable that these two specific characters evolved only once in the genus Emertonia. Their apparently cosmopolitan distribution covers thousands of kilometres and spans all major oceans. This biogeographical pattern may be explained by resuspension events followed by passive transport by benthic currents. Discrepancies in their dispersal ranges may be a result of changing geological and oceanographic boundaries.

El Niño–Southern Oscillation signal in a new East Antarctic ice core, Mount Brown South

Abstract. Paleoclimate archives, such as high-resolution ice core records, provide a means to investigate past climate variability. Until recently, the Law Dome (Dome Summit South site) ice core record remained one of few millennial-length high-resolution coastal records in East Antarctica. A new ice core drilled in 2017/2018 at Mount Brown South, approximately 1000 km west of Law Dome, provides an additional high-resolution record that will likely span the last millennium in the Indian Ocean sector of East Antarctica. Here, we compare snow accumulation rates and sea salt concentrations in the upper portion (∼ 20 m) of three Mount Brown South ice cores and an updated Law Dome record over the period 1975–2016. Annual sea salt concentrations from the Mount Brown South site record preserve a stronger signal for the El Niño–Southern Oscillation (ENSO; austral winter and spring, r = 0.533, p &lt; 0.001, Multivariate El Niño Index) compared to a previously defined Law Dome record of summer sea salt concentrations (November–February, r = 0.398, p = 0.010, Southern Oscillation Index). The Mount Brown South site record and Law Dome record preserve inverse signals for the ENSO, possibly due to longitudinal variability in meridional transport in the southern Indian Ocean, although further analysis is needed to confirm this. We suggest that ENSO-related sea surface temperature anomalies in the equatorial Pacific drive atmospheric teleconnections in the southern mid-latitudes. These anomalies are associated with a weakening (strengthening) of regional westerly winds to the north of Mount Brown South that correspond to years of low (high) sea salt deposition at Mount Brown South during La Niña (El Niño) events. The extended Mount Brown South annual sea salt record (when complete) may offer a new proxy record for reconstructions of the ENSO over the recent millennium, along with improved understanding of regional atmospheric variability in the southern Indian Ocean, in addition to that derived from Law Dome.

Purification of Disc-Shaped Diatoms from the Southern Ocean Sediment by a Cell Sorter to Obtain an Accurate Oxygen Isotope Record

The oxygen isotopic composition (δ18O) of diatom frustules is potentially a quantitative paleoenvironmental proxy. However, δ18O analysis has some uncertainties because of difficulties in removing clay-mineral contamination and taxon-specific separation due to the small size of diatom frustules. The clay-mineral contamination seriously affects δ18O measurements, and the δ18O of bulk diatoms contains a mixture of information from diatoms living in various seasons and water depths. To resolve such problems, we established a new method for purifying the frustules of disc-shaped diatoms using a cell sorter and succeeded in removing the clay-mineral contamination and restricting the number of species for the δ18O analysis. We developed this method using samples from a sediment core retrieved from the Conrad Rise in the Indian Ocean sector of the Southern Ocean. First, the disc-shaped diatoms were enriched and cleaned by sieving, elutriation, and heavy-liquid separation. The samples were then further purified by a cell sorter. Regardless of the diatom assemblage or the sediment type in the core sample, this method generated samples consisting of more than 95% disc-shaped diatoms, dominated by Thalassiosira lentiginosa (Janisch) Fryxell, which occurs ubiquitously throughout the Southern Ocean. The δ18O profile for the sediment core obtained from purified disc-shaped diatoms showed the last glacial cycle since ca. 40 ka, which can be correlated with the LR04 benthic δ18O stack record and the temperature record in the EPICA Dome C ice core, indicating that this method can contribute to obtaining an accurate δ18O record of diatoms associated with glacial–interglacial cycles.

Record‐Low WNP Tropical Cyclone Activity in Early Summer 2020 due to Indian Ocean Warming and Madden‐Julian Oscillation Activity

AbstractDuring early boreal summer 2020, the western North Pacific (WNP) was characterized by record‐low tropical cyclone (TC) activity, reaching the lowest historical level since 1979. Only one short‐lived TC was observed in June and the whole of July underwent an unprecedented quiescent TC period. Concurrent Indian Ocean warming provided unfavorable conditions for cyclogenesis over the WNP, which partly (∼40%) explains the extremely low TC number from a statistical standpoint. Accompanied with the Indian Ocean warming, an unprecedentedly long‐lasting Madden‐Julian Oscillation (MJO) event stalled over the Indian Ocean sector, persisting almost through the entire June and July. This simultaneous quasi‐stationary MJO activity further caused unfavorable background conditions for cyclogenesis in the WNP. The Indian Ocean warming combined with the anomalous MJO conditions together largely (&gt;80%) explain the record‐low TC number over the WNP during early summer 2020.

Impact of the Antarctic topography on meridional energy transport and its consequential effect in the monsoon circulation

AbstractAntarctica has been losing ice in the past, and its ice loss is projected to further enhance in the future due to global warming, causing orographic changes over the region. Such orographic changes are likely to profoundly influence the global climate systems through energy transport over the Southern Hemisphere. The South Asian monsoon system, an anomalous climate system (a transient eddy regionally occurring rigorously during JJAS) originating in the Southern Hemisphere and transporting anomalous energy towards higher latitudes, is also expected to get influenced by its orography. A coupled global climate modelling framework is therefore used in this study to investigate the potential influence of the Antarctic orography on the South Asian monsoon system. The investigation reveals that a reduction in the Antarctic elevation would cause warming over the continent, which will cause changes in the energy budget, with more outgoing long‐wave radiation over Antarctica due to a warmer surface and moist atmosphere aloft. The global climate responds to this perturbation by enhancing the southward energy transport primarily by the atmospheric component via changes in mean flow and eddies from the equatorial region all the way to the South Pole. The monsoon system supports this southward energy transport demand in the Southern Hemisphere by strengthening the mean meridional circulation in the three cells over the Indian Ocean sector. Due to this, the low‐level cross‐equatorial flow enhances over the south equatorial Indian Ocean, which increases the evaporation, and causes changes in precipitation and stationary wave patterns. The sea‐level pressure and surface temperature changes adjust accordingly in response to changes in the circulation. However, rainfall and circulation over the Asian landmass do not change much as the southward energy transport is very much less and is mostly supported by the oceanic components and changes in latent energy over these latitudes.

Excess ice loads in the Indian Ocean sector of East Antarctica during the last glacial period

Abstract An accurate reconstruction of the Antarctic Ice Sheet is essential in order to develop an understanding of ice-sheet responses to global climate changes. However, the erosive nature of ice-sheet expansion and the difficulty of accessing much of Antarctica make it challenging to obtain field-based evidence of ice-sheet and sea-level changes before the Last Glacial Maximum. Limited sedimentary records from Lützow-Holm and Prydz Bays in East Antarctica demonstrate that the sea level during Marine Isotope Stage 3 was close to the present level despite the global sea-level drop lower than −40 m. We demonstrate glacial isostatic adjustment modeling with refined Antarctic Ice Sheet loading histories. Our experiments reveal that the Indian Ocean sector of the Antarctic Ice Sheet would have been required to experience excess ice loads before the Last Glacial Maximum in order to explain the observed sea-level highstands during Marine Isotope Stage 3. As such, we suggest that the Antarctic Ice Sheet partly reached its maximum thickness before the global Last Glacial Maximum.

Variation of particulate organic matter characteristics in the upper water column of eddy-influenced waters at the subtropical front of the Indian sector of the Southern Ocean

Mesoscale eddies influence the nutrient distribution and modulate the phytoplankton growth. The present study addressed the influence of cyclonic and anticyclonic eddies on the variability of particulate organic matter composition at the Subtropical Front of the Indian Ocean sector of the Southern Ocean during austral summer 2012 and 2013. It was observed that the concentration of particulate organic carbon was lower at the aged cyclonic eddy (29.62 to 59.42 μg/L) compared to that observed at the freshly formed cyclonic eddies (36.03 to 194.19 μg/L). Likewise, at the matured anticyclonic eddies the particulate organic carbon was comparatively lesser (15.10 to 58.94 μg/L) than that noted at the freshly formed eddy (29.54 to 104.44 μg/L). The isotopic signatures of POM (δ13C(POM) & δ15N(POM)) were significantly different at the eddy regions. An enrichment of δ13C(POM) was observed at the surface of cyclonic eddies with the highest δ13C(POM) (−21.40‰) at a ~ 3 month old cyclonic eddy. However, an enrichment of δ15N(POM) was observed at the depth of deep chlorophyll maxima of anticyclonic eddies with the highest δ15N(POM) (4.39‰) at the ~2 month old anticyclonic eddy. The variability in the POM characteristics and the dominant biochemical processes during this study were attributed to the difference in the eddy properties such as age, intensity and its origin. The study also indicated that eddy properties and the associated upwelling and downwelling processes altered the nutrient dynamics and supported a shift in the biological community structure that played a significant role in the variability of POM characteristics at the eddy influenced regions like the Subtropical Front.