Sea Sector Research Articles

Delineating Polynya Area Using Active and Passive Microwave Sensors for the Western Ross Sea Sector of Antarctica

A polynya is an area of open water or reduced concentration of sea ice surrounded by either concentrated sea ice or land ice. They are often seen as sites of intense ocean–atmosphere heat exchange and as ice production factories. Given their importance, it is crucial to quantify the accuracy of satellite-derived polynya information. Polynyas in their early evolution phase are generally narrow and occur at scales likely too fine to be detected by widely used passive microwave (PMW) radiometric sensors. We derived 40 m scale polynya information over the western Ross Sea from high-resolution Synthetic Aperture Radar (SAR) Sentinel-1 C-band data and examined discrepancies with larger-scale estimates. We utilized two automated algorithms, supervised (a rule-based approach) and unsupervised (a combination of texture analysis with k-means clustering), to accurately identify the polynya areas. We generated data for validation using Sentinel-1 data at instances where polynyas can be visually delineated. Results from PMW sensors (NSIDC and AMSR2) and SAR-based algorithms (rule-based and texture-based) are compared with manually delineated polynya areas obtained through Sentinel-1. Analysis using PMW sensors revealed that NSIDC overestimates larger polynyas and underestimates smaller polynyas compared to AMSR2. We were more accurately able to identify polynya presence and area using Sentinel-1 SAR observations, especially in clear cases and cases when PMW data miscalculates the polynya’s presence. Of our SAR-based algorithms, the rule-based approach was more accurate than the texture-based approach at identifying clear polynyas when validated against manually delineated regions. Altogether, we emphasize the need for finer spatio-temporal resolution data for polynya studies.

Change at 85 degrees south: Shackleton Glacier region proglacial lakes from 1960 to 2020

Abstract Over the last two decades, anomalous warming events have been observed in coastal Antarctic regions. While these events have been documented in the Ross Sea sector, the Antarctic interior is believed to have been buffered from warming. In this work, we present data from lakes located near Mt. Heekin and Thanksgiving Valley (~85° S) along the Shackleton Glacier, which are believed to be the southern-most Antarctic dry valley lakes. In 2018, the lakes were characterized, repeat satellite images were examined, and lake water chemistry was measured. Our analysis shows that lake areas recently increased, and the water-soluble ion chemistry indicates a flushing of salts from periglacial soils, likely from increased glacial melt as illustrated by water isotope data. Our results show that high southern latitude ice-free areas have likely been affected by warm pulses over the past 60 years and these pulses may be quasi-synchronous throughout the Transantarctic Mountains.

Reconstructing Continuous Ice Sheet Elevation Changes in the Amundsen Sea Sector During 2003–2021 by Merging Envisat, ICESat, CryoSat‐2, and ICESat‐2 Multi‐Altimeter Observations

AbstractThe Amundsen Sea (AS) sector in West Antarctica accounts for a significant proportion of Earth's ice losses and is the largest contributor of Antarctica's mass loss. To evaluate its contribution to global sea‐level rise, we reconstruct the long‐term continuous surface elevation changes (CSEC) record of the AS sector by an improved least‐squares plane fitting method (ILSPFM), which merged the relative surface elevation change (SEC) series instead of height from Envisat, ICESat, CryoSat‐2, and ICESat‐2 missions during 2003–2021. The accuracy of CSEC is improved by 25.9% using ILSPFM. The average rate of CSEC in the AS sector was −24.25 ± 0.48 cm yr−1 during 2003–2021. The largest signals of SEC are found over Pine Island, Thwaites, and Pope Glaciers, with the largest decline of SEC over Pope Glacier with a total SEC of −82.44 ± 7.21 m and an annual change rate of −4.34 ± 0.38 m yr−1. The ridge between Pine Island and Thwaites Glaciers is found in the AS sector, indicating that the change of ice sheet is dynamic thinning and closely related to the topography and the distance from the grounding line. Compared with meteorological data sets, we find that the codirectional fluctuation in CSEC is delayed by 3 months with surface temperature, and the precipitation leading SEC series as the phase arrow points straight down from the cross wavelet transform. Our new record shows that the AS sector thinned rapidly from 2003 to 2021 but decelerated from 2019 to 2021, and it was clearly correlated to the surface temperature, precipitation, and local terrain.

High mid-Holocene accumulation rates over West Antarctica inferred from a pervasive ice-penetrating radar reflector

Abstract. Understanding the past and future evolution of the Antarctic Ice Sheet is challenged by the availability and quality of observed paleo-boundary conditions. Numerical ice-sheet models often rely on these paleo-boundary conditions to guide and evaluate their models' predictions of sea-level rise, with varying levels of confidence due to the sparsity of existing data across the ice sheet. A key data source for large-scale reconstruction of past ice-sheet processes are internal reflecting horizons (IRHs) detected by radio-echo sounding (RES). When IRHs are isochronal and dated at ice cores, they can be used to determine paleo-accumulation rates and patterns on large spatial scales. Using a spatially extensive IRH over the Pine Island Glacier (PIG), Thwaites Glacier (THW), and the Institute and Möller ice streams (IMIS, covering a total of 610 000 km2 or 30 % of the West Antarctic Ice Sheet (WAIS)), and a local layer approximation model, we infer mid-Holocene accumulation rates over the slow-flowing parts of these catchments for the past ∼4700 years. By comparing our results with modern climate reanalysis models (1979–2019) and observational syntheses (1651–2010), we estimate that accumulation rates over the Amundsen–Weddell–Ross Divide were on average 18 % higher during the mid-Holocene than modern rates. However, no significant spatial changes in the accumulation pattern were observed. The higher mid-Holocene accumulation-rate estimates match previous paleo-accumulation estimates from ice-core records and targeted RES surveys over the ice divide, and they also coincide with periods of grounding-line readvance during the Holocene over the Weddell and Ross sea sectors. We find that our spatially extensive, mid-Holocene-to-present accumulation estimates are consistent with a sustained late-Holocene period of higher accumulation rates occurring over millennia reconstructed from the WAIS Divide ice core (WD14), thus indicating that this ice core is spatially representative of the wider West Antarctic region. We conclude that future regional and continental ice-sheet modelling studies should base their climatic forcings on time-varying accumulation rates from the WAIS Divide ice core through the Holocene to generate more realistic predictions of the West Antarctic Ice Sheet's past contribution to sea-level rise.

Oil and gas potential and modern seismicity of the Azerbaijan sector of the Caspian Sea

Hydrocarbon deposits of the Republic of Azerbaijan are located in the South-Caspian oil and gas basin, on the territory of the Absheron Peninsula and the adjacent waters of the Caspian Sea. There are more than 80 oil and gas fields here. For this purpose, this article presents the geological structure of the South Caspian Depression, as well as the Apsheron-Pribalkhansk zone. Conducted analysis of oil and gas reserves and modern seismicity of the Caspian Sea. Increase in recoverable oil reserves, stabilization of mining at this stage — the task number is one for the oil field. It has been established that in recent years the level of seismic activity in certain areas of the Caspian Sea has risen, and the amount of seismic energy released in the Central Caspian Sea has increased by several dozen times. Distribution of density of epicenters in the whole alpine part of the region carries a weakly expressed wave character, which is represented by an alternation of differentiated zones of elevated and lowered concentration of epicenters. Zones have a predominantly north-western, submeridional and subshirot space. To determine the regularity of the distribution of hypocenter centers in the region, a diagram of the dependence of the number of earthquakes on the depths was built. In the waters of the Caspian Sea, 90 % of the hypocenters are located at a depth of more than 35 km. Together with them meet and close surface earthquakes. It was assumed that the change in the flow of oil in many seabed areas of the northern part of the Absheron-Balkhan storage system is associated with strong (ml>3.0) earthquakes of characteristic type. Besides, there was a schematic model, which characterizes the formation of oil and gas fields in the structures, caused by the stress on the local area. The formation of the zone of localization of oil is associated with the accumulation of stresses in the local geodynamic fields and the formation of cracked media, although in such areas there is a gap, the probability of migration of hydrocarbons and hydrocarbons. On the basis of the above, it is possible to assume that there is a definite regularity between the oil and gas fields and seismicity in one and the same interval.

Mass Balance of the Antarctic Ice Sheet in the Early 21st Century

Mass loss from the Antarctic Ice Sheet (AIS) is an important contributor to global sea level rise. To examine the recent ice loss, we estimated the mass budget of the AIS from 2000 to 2020 using multiple ice velocity datasets, state-of-the-art ice thickness datasets, and extended surface mass balance (SMB) records. The AIS lost mass at an average rate of −89 ± 99 Gt/yr over the study period. The East Antarctic Ice Sheet (EAIS) showed a slightly positive mass balance, while the West Antarctic Ice Sheet (WAIS) experienced a significant acceleration in mass loss. The ice discharge from the AIS increased from 1792 ± 47 Gt/yr in 2000 to 1940 ± 37 Gt/yr in 2017–2020, with the increase in the discharge from the WAIS being three to four times higher than that from the EAIS. Moreover, the average mass balance for 2017–2020 was −99 ± 93 Gt/yr, slightly more negative than the average for the early 21st Century. During this recent period, the ice discharge decreased in the East Indian Ocean sector, in contrast to its rapid increase from 2000 to 2013–2017. However, the discharge in the Amundsen Sea sector still greatly increased from 2013–2017 to 2017–2020. Overall, our results are in agreement with recent mass balance estimates for the AIS based on gravimetry and altimetry. Our assessments of the recent AIS mass balance with the mass budget method (input-output method) will contribute to the understanding of ice dynamic processes and provide insights into the stability of the AIS.

Hydrocarbon systems in the Turkmen sector of the South Caspian basin

Introduction. The paper considers conditions conductive to the formation and location of oil and gas accumulations in the Turkmen sector of the South Caspian Basin.Aim. Modeling of hydrocarbon systems of the Turkmen sector of the South Caspian Basin.Materials and methods. Statistical generalization and systematization of the data and materials presented in reference literature, field sources, and archive data, as well as published works of Sh.F. Mekhtiev, I.S. Guliev, M.Z. Rachinskii, S.S. Dzhibuti, S.A. Aliev, V.Yu. Kerimov, V.V. Kolodiya, etc. Data modeling was performed using the PetroMod software.Results. As a result of numerical modeling, the formation conditions of hydrocarbon systems and their main elements, i.e., oil and gas source strata (OGSS), reservoirs and seals, were determined. Oil and gas prospects were identified, and the main spatial and temporal patterns in the development of generation, migration, and accumulation processes of hydrocarbon fluids, as well as the formation conditions of traps were established. In addition, a map was created to illustrate potential prospective zones, objects, and “plays.” Oil-and-gas prospects were determined, and the main areas of oil-and-gas exploration in the Turkmen sector of the Caspian Sea were substantiated.

Recent Warming Trends in the Arabian Sea: Causative Factors and Physical Mechanisms

In recent years, and particularly from 2000 onwards, the North Indian Ocean (NIO) has been acting as a major sink of ocean heat that is clearly visible in the sub-surface warming trend. Interestingly, a part of the NIO—the Arabian Sea (AS) sector—witnessed dramatic variations in recent sub-surface warming that has direct repercussion on intense Tropical Cyclone (TC) activity. This study investigated the possible causative factors and physical mechanisms towards the multi-decadal warming trends in surface and sub-surface waters over the AS region. Responsible factors towards warming are examined using altimetric observations and reanalysis products. This study used ORAS5 OHC (Ocean Heat Content), derived meridional and zonal heat transport, currents, temperature, salinity, Outgoing Longwave Radiation (OLR), and air-sea fluxes to quantify the OHC build-up and its variability at water depths of 700 m (D700) and 300 m (D300) during the past four decades. The highest variability in deeper and upper OHC is noticed for the western and southern regions of the Indian Ocean. The warming trend is significantly higher in the deeper regions of AS compared to the upper waters, and relatively higher compared to the Bay of Bengal (BoB). Increased OHC in AS show good correlation with decreased OLR in the past 20 years. An analysis of altimetric observations revealed strengthening of downwelling Kelvin wave propagation leading to warming in eastern AS, mainly attributed due to intrusion of low saline water from BoB leading to stratification. Rossby wave associated with deepening of thermocline warmed the southern AS during its propagation. Heat budget analysis reveals that surface heat fluxes play a dominant role in warming AS during the pre-monsoon season. Increasing (decreasing) trend of surface heat fluxes (vertical entrainment) during 2000–2018 played a significant role in warming the southeastern sector of AS.

PENGAWASAN DEWAN PERWAKILAN RAKYAT DAERAH TERHADAP PENDAPATAN ASLI DAERAH PADA SEKTOR PERHUBUNGAN LAUT DAN DARAT DI KABUPATEN BUTON TENGAH

The purpose of this study was to determine the implementation of the DPRD’s supervisory function on PAD in Central Buton Regency and the obstacles in the DPRD’ supervisory function of PADin central Buton Regency. This research is a type of normative juridical research with a law approach which takes place in ino month in Central Buton Regency. The result of this study indicate that: (1) DPRD’s supervisory function of PAD can be divided into two, namely, supervision carried out oytside the DPRD building and supervision carried out outside the DPRD building and supervision carried out inside the DPRD building ; (2) The obstacles are DPRD members who lack adequate intellectual abilities, adequate levels of education, education levwls which have implication for the less than optimal role of DPRD, both institutional and individual roles, and lack of human resources in the sea and land transportation sector. The research suggests: DPRD members in carrying out their supervision must have intellectual abilties, further improve education and must increase adequate human resources

Strong regionalism in dinoflagellate cysts in recent sediments from the Chukchi-East Siberian Seas, Arctic Ocean

The Pacific sector of the Arctic Ocean, a region with the fastest sea-ice loss in recent decades, is experiencing unprecedented biological regime shifts in its marine ecosystems today. However, a shelf-wide characterization of marine plankton communities over this region and environmental processes behind it remain largely unresolved, despite phytoplankton phenology is now considered to be an important factor for assessing how Arctic Ocean interacts with global climate change. Here, we present the first detailed description of recent dinoflagellate cyst assemblages in 32 surface sediment samples from the Chukchi–East Siberian Sea shelves, the Pacific Arctic Ocean, to examine their biogeographic patterns and associated environmental forcing factors. We find a strong regionalization in the species composition and distribution along the shallow-shelf cyst accumulation zone; in the Chukchi Sea sector, northward flow of warm-Pacific water along with extreme seasonality, sufficient nutrient supplies and higher light availability leads to a large occupation of cosmopolitan, opportunistic-nature taxa, whilst the East Siberian Sea sector with more extensive sea-ice cover and lower temperatures is primarily dominated by “round brown spiny cyst” taxa that have a strong affinity for cold, polar conditions. Specifically, an exclusive dominance of heterotrophic taxa at the East Siberian Sea region is inferred to be closely tied to Atlantic-origin water intrusions that lift nutrient-rich, cold bottom water up to oligotrophic surface layer to grow diatoms and other prey organisms. The observed contrast in this geographical “hot spot”, where the Pacific- and Atlantic-origin waters face each other, clearly manifests a growing expansion of southern waters into an increasingly ice-free Arctic Ocean that reshapes Arctic Ocean biogeography from the base of marine food chains. Our study highlights considerable potential of dinoflagellate cysts as a valuable environmental proxy to indicate complex interactions between ocean physics and marine biology under the rapidly changing Arctic climate system.

Sedimentological features of asbestos cement fragments in coastal environments (Taranto, southern Italy)

Asbestos cement materials (ACMs) are widespread in coastal environments as result of illegal dumping activities. This study focuses on the Taranto area (Italy) in the Mar Grande basin within the northern sector of the Ionian Sea. The complex history of dumping building materials containing high amounts of ACM into the coastal zone, and the erosion, transport and deposition in Marechiaro Bay is a serious environmental hazard. An interdisciplinary research methodology defines the temporal dumping succession, and the erosional processes and phases, the diffusion of ACM, the mineralogical characteristics, and existing physical status of the ACM. A multiscale investigation was conducted. Results show that from 1992 to 2000 a significant increment of dumping operations have occurred. The current cliff has been subject to erosion and redeposition phases, developing a new beach composed of these polluted man-made sediments. The findings persuade the local authorities to close the beach requiring remediation interventions.

TECHNICAL STUDY OF PT XYZ SHIPPING FLOW OF COAL BARGE TO INCREASE DWT (DEADWEIGHT TONNAGE) CAPACITY FROM 5,000 DWT TO 10,000 DWT

Coal is one of the important energy source commodities to carry out industrial activities, which require supporting infrastructure that uses shipping lanes as a means of activity in the delivery of coal from producers to consumers. PT XYZ, in this case as a coal producer, has allocated one of the areas used for coal loading facilities from one of the coal mining located in Gurimbang Village, Sambaliung District, Berau Regency, East Kalimantan Province by using the Berau river channel to the transshipment location in Muara Pantai, Pulau Derawan District, Berau Regency. PT XYZ has obtained a Terminal Permit for Own Interests in the Working Environment and Interest Areas of Tanjung Redeb Port to Support Business Activities in the Coal Mining Sector PT XYZ “TUKS” through the Decree of the Director General of Sea Transportation Number: BX-144/PP 008 concerning Approval Terminal Management for Own Interests in the Work Environment Area and Interest Area of Tanjung Redeb Port to Support Business Activities in the Coal Mining Sector with a capacity of 5,000 DWT. Based on the results of the study of the TUKS flow plan, the position of the general shipping lane, the bathymetry survey of the barge path, the depth of the TUKS pool, the planned loading and unloading volume, the dimensions of the ship that will dock and unload, the frequency of ship visits, the availability of Shipping Navigation Assistance Facilities (SBNP), as well as observations at several points that will become obstacles in shipping navigation, it can be concluded that the development/increase of the DWT TUKS Gurimbang capacity of PT XYZ to support operational activities is still safe enough to be increased to a payload capacity of 8,000 MT with a maximum draft of submerged ships/barges at a depth of -4.70 meters. Therefore, this research can be continued for the preparation of technical review documents as a requirement to fulfill PM 89 of 2018 concerning Norms, Standards, Procedures, and Criteria for Electronically Integrated Business Licensing for the Transportation Sector in the Sea Sector in the process of adjusting DWT (Dead Weight Tonnage) at the Terminal for Self Interest/TUKS PT XYZ in Gurimbang Village.

КРЕЙДОВИЙ РИФТОГЕНЕЗ У ГЕОЛОГІЧНІЙ ІСТОРІЇ УКРАЇНСЬКОГО СЕКТОРУ ЧОРНОГО МОРЯ

Within the Ukrainian sector of the Black Sea, the Albian-Cenomanian rift faults formed three large rift basins, which consisted of a system of grabens and half-grabens. One of the sublatitude rift basins occupied the modern Karkinit Trough, Krylov-Zmiiny Uplift, Gubkin Ridge and the Sulina Depression on the Odesa Shelf. The second sublatitude basin occupied the modern Tetyaev High, Sorokin Trough, Marine Continuation of the Crimean Folds and, apparently, the Crimean Mountains. The third rift basin extended from the northwest to the southeast and encompassed the Euxinian Graben, Andrusov Ridge, Eastern Black Sea Basin, and Shatskiy High. The greatest depth of the base of the rift sequence is observed in the central part of the Western Black Sea Basin, where it is 15.5–16.5 km. In the Eastern Black Sea basin, the maximum depth is 12.5–13.5 km. The shallowest depths of the base of the rift sequence are characteristic of the Kalamit Swell and the Marine Continuation of the Crimean Folds. During the Cenozoic phases of compression, almost all rift (half)grabens underwent intense folding and vertical movements from several hundreds of meters to 4–5 km. At the same time, most of the rift faults underwent partial or complete inversion.

ПОЛИАРОМАТИЧЕСКИЕ УГЛЕВОДОРОДЫ В ДОННЫХ ОТЛОЖЕНИЯХ КАСПИЙСКОГО МОРЯ

In this study, variations in the levels of oil hydrocarbons and polycyclic aromatic hydrocarbons (PAHs), which are persistent organic pollutants generated by human activities, were assessed in the bottom sediments of the Caspian Sea (Russia) sampled from 2012 to 2021. The samples were analyzed for their chemical composition. The concentrations of the identified compounds responsible for hydrocarbon pollution were established. The quantitative results of the industrial environmental monitoring in the Russian sector of the Caspian Sea for subsoil use were also reviewed and processed by standard statistical methods. It was revealed that ΣPAH concentrations in the Northern and Middle Caspian Sea regions vary from analytical zero to 186.7 μg/kg and from zero to 467.8 μg/kg, respectively. The scale of oil pollution in these two regions was found to be determined by the following PAHs: phenanthrene, acenaphthene, and naphthalene. The origin of the listed PAHs provides vital information on the main sources of pollution of the Caspian Sea bottom sediments with hazardous organic substances. Based on the obtained data, the areas with background PAH pollution of the bottom sediments and those with the characteristic PAH of mainly natural and pyrogenic origin were located.

Evaluation of Suspended Matter Content in the Coastal Zone of the Northeastern Part of the Black Sea by Relative Transparency

Based on the materials of 20 expeditions of the IO RAS conducted in various areas of the coastal zone of the Russian sector of the Black Sea in the period from 1999 to 2021, empirical equations the relationship between the relative transparency (depth of visibility of the white disk Zd) and the mass concentrations of the total suspended matter-SM and its mineral – SMM and organic – POM fractions (Csm, Csmm and Csom, respectively) were obtained. The values of Zd were recorded in the range from 0.1 to 21 m, the concentrations of SMM – from 0.11 to 104 mg/L, POM – from 0.09 to 2.0 mg/l and chlorophyll a (Ca) – from 0.03 to 4.4 mcg/l. The relative abundance of the POM in the suspension ranged from 1.1 to 48.7%. The estimation of the error in the calculations according to these equations is carried out. The coefficients of determination r2 = 0.85 (for lgCsm and lgCsmm ) and 0.72 ( for lg Csom). The influence of the concentration of POM – on the accuracy of the calculation of Csmm and the concentration of chlorophyll a on the accuracy of the calculation of Csom was revealed. It is concluded that it is possible to use empirical formulas related to the entire array to calculate the concentrations of these fractions of suspension in the entire studied water area. It is proposed to consider the method of estimating the content of suspension fractions based on the obtained empirical equations as a regional variant of the method of passive sounding of the upper layer of the sea using a white disk.

Digital Design of Modern Equipment for Measuring Geodynamics and Seismicity of the Azerbaijan Sector of the Caspian Sea

Digital Design of Modern Equipment for Measuring Geodynamics and Seismicity of the Azerbaijan Sector of the Caspian Sea

Age assessment of the Jasmund Glacitectonic Complex (SW Baltic Sea) by quartz luminescence dating of syn-kinematic deposits

The development of the Fennoscandian Ice Sheet (FIS) in its SW Baltic Sea sector during MIS 2 led to the formation of the Jasmund Glacitectonic Complex (JGC). The evolutional stages of the latter reflect small-dimensioned ice sheet oscillations. A glacitectonically formed piggyback basin is in focus to give direct information on the evolution of the JGC. We present a set of five OSL ages from syn-kinematic glacilacustrine and alluvial fan sediments deposited between ice margin-parallel thrust-bounded ridges from the southern margin of the JGC. The ice front proximal depositional environment and short transport distances of the sediments implicate a possible insufficient bleaching of the luminescence signal. Nonetheless, we were able to gain reliable ages of ~22 ka for the growth of the southern JGC. The samples pre-date the Oder ice stream reaching its maximum extent, the Pomeranian ice marginal belt at ~18–20 ka. A comparison of our data with the existing age data related to the evolution of the JGC will contribute to a better understanding of the FIS dynamics in the research area and the timing of the Pomeranian phase in NE Germany.

Modern geodynamics and seismicity of the Azerbaijani sector of the Caspian Sea

The region’s oil fields are located within the South Caspian oil and gas basin, on the territory of the Absheron Peninsula and the adjacent waters of the Caspian Sea. Here are more than 80 oil and gas fields. To this end, this article presents the geological structure of the South Caspian Depression, as well as the Absheron-Balkhan zone. The analysis of oil and gas content and modern seismicity of the Caspian Sea is carried out. Increasing recoverable oil reserves, reducing water cut, increasing or even stabilizing production at this stage is the number one task for the oil industry. It has been established that in recent years, the level of seismic activity of individual sections of the Caspian water area has increased, and the amount of seismic energy released in the Central Caspian has increased by several dozen times, it can be assumed that the change in oil production in many offshore fields in the northern part of the Absheron-Balkhan fold system is associated with strong (ml>3.0) earthquakes characterized by fault-shear type of movements. Keywords: Caspian sea; oil and gas deposits; earthquake source mechanisms.

Drivers and Reversibility of Abrupt Ocean State Transitions in the Amundsen Sea, Antarctica

AbstractOcean warming around Antarctica has the potential to trigger marine ice‐sheet instabilities. It has been suggested that abrupt and irreversible cold‐to‐warm ocean tipping points may exist, with possible domino effect from ocean to ice‐sheet tipping points. A 1/4° ocean model configuration of the Amundsen Sea sector is used to investigate the existence of ocean tipping points, their drivers, and their potential impact on ice‐shelf basal melting. We apply idealized atmospheric perturbations of either heat, freshwater, or momentum fluxes, and we characterize the key physical processes at play in warm‐to‐cold and cold‐to‐warm climate transitions. Relatively weak perturbations of any of these fluxes are able to switch the Amundsen Sea to an intermittent or permanent cold state, that is, with ocean temperatures close to the surface freezing point and very low ice‐shelf melt rate. The transitions are reversible, that is, canceling the atmospheric perturbation brings the ocean system back to its unperturbed state within a few decades. All the transitions are primarily driven by changes in surface buoyancy fluxes resulting from the freshwater flux perturbation or from modified net sea‐ice production due to either heat flux or sea‐ice advection anomalies. These changes affect the vertical ocean stratification over the continental shelf and thereby the eastward undercurrent at the shelf break, which both impact ice‐shelf melting. As sea‐ice induced deep convection is already quite limited in present‐day conditions, surface buoyancy gain in a warmer climate has relatively little effect on deep ocean properties compared to colder climate conditions.

West Antarctic Ice Sheet Dynamics in the Amundsen Sea Sector since the Late Miocene—Tying IODP Expedition 379 Results to Seismic Data

Observations of rapid ongoing grounding line retreat, ice shelf thinning and accelerated ice flow from the West Antarctic Ice Sheet (WAIS) may forebode a possible collapse if global temperatures continue to increase. Understanding and reconstructing West Antarctic Ice Sheet dynamics in past warmer-than-present times will inform about its behavior as an analogue for future climate scenarios. International Ocean Discovery Program (IODP) Expedition 379 visited the Amundsen Sea sector of Antarctica to obtain geological records suitable for this purpose. During the expedition, cores from two drill sites at the Resolution Drift on the continental rise returned sediments whose deposition was possibly influenced by West Antarctic Ice Sheet dynamics from late Miocene to Holocene times. To examine the West Antarctic Ice Sheet dynamics, shipboard physical properties and sedimentological data are correlated with seismic data and extrapolated across the Resolution Drift via core-log-seismic integration. An interval with strongly variable physical properties, high diatom abundance and ice-rafted debris occurrence, correlating with partially high amplitude seismic reflection characteristics was identified between 4.2 and 3.2 Ma. Sedimentation during this interval is interpreted as having occurred during an extended warm period with a dynamic West Antarctic Ice Sheet in the Amundsen Sea sector. These records compare to those of other drill sites in the Ross Sea and the Bellingshausen Sea, and thus suggest an almost simultaneous occurrence of extended warm periods in all three locations.