Drake Passage Research Articles

Regionally distinct drivers of the carbonate system dynamics in the Drake Passage and northern Antarctic Peninsula

Regionally distinct drivers of the carbonate system dynamics in the Drake Passage and northern Antarctic Peninsula

Spatial variability of marine carbonate system along the Drake Passage and northern Antarctic Peninsula during the austral summer

Spatial variability of marine carbonate system along the Drake Passage and northern Antarctic Peninsula during the austral summer

Response of Australian Summer Monsoon Precipitation to a Strengthening Antarctic Circumpolar Current

AbstractThe Australian summer monsoon (AUSM) is the strongest monsoon in the Southern Hemisphere and it is greatly influenced by the climate conditions in the Indo‐Pacific and adjacent regions. Inspite of the substantial studies of the monsoon, the linkage between the AUSM and the high‐latitude Southern Ocean climate has not been fully understood. This study investigates how AUSM rainfall is affected by the Antarctic Circumpolar Current (ACC) by simulating scenarios with a closed and an opened Drake Passage with the Community Earth System Model. It is found that AUSM precipitation decreases as a result of reduced local humidity caused by a strengthening ACC. An opened Drake Passage leads to strengthening ACC and Atlantic Meridional Overturning Circulation, which in turn creates an El Niño‐like state in the Pacific. This weakens the Walker Circulation, resulting in reduced local moisture, anomalous subsidence over the AUSM region, and a subsequent decrease in monsoon precipitation.

The Initial Opening of the Drake Passage Occurred During ca. 62‐59 Ma

AbstractAlthough the Drake Passage has been considered a critical component of ocean circulation and climate, its initial opening age remains controversial due to the weak constraints on the paleoposition of the Antarctic Peninsula. Here, new zircon U‐Pb geochronological studies are conducted on the Barchans Islands, providing a critical age constraint on the paleopole (Latitude = 76.9°S, Longitude = 332.1°E, A95 = 5.9°) of the peninsula at ca. 59 Ma. Geochronological and paleomagnetic studies on Anagram Island and King George Island provide a new paleopole (Latitude = 77.4°S, Longitude = 23.5°E, A95 = 4.4°) of the Antarctic Peninsula at ca. 55 Ma. When combined with existing evidence, the initial separation between the Antarctic Peninsula and the Patagonian Andes is restricted to be between ca. 62 and 59 Ma, caused by the clockwise rotation of the Antarctic Peninsula. The separation induced the initial opening of the Drake Passage and the formation of the shallow proto‐Antarctic circumpolar current, as well as Paleocene global cooling.

Impacts of Strengthened Antarctic Circumpolar Current on the Seasonality of Arctic Climate

AbstractTo understand the role of the Antarctic Circumpolar Current (ACC) in the polar seasonality and its remote effect on the Arctic climate, we use the Community Earth System Model to perform Drake Passage (DP) open and closed experiments. Model results illustrate that in the opened DP, the ACC and Atlantic Meridional Overturning Circulation (AMOC) strengthen, leading to a colder Antarctic and a warmer Arctic. Notably, the temperature changes in both the Antarctic and the Arctic show significant seasonal differences, with the largest polar response during the cold seasons. Around the Antarctic, both the ACC and overturning circulation exhibit stronger acceleration in winter than in summer, causing more pronounced cooling in winter. Furthermore, negative seasonal energy transfer mechanism amplifies this cooling. In contrast, around the Arctic, the AMOC and ocean heat transport show relatively insignificant seasonal variation. Instead, it is the downward latent and sensible fluxes that induce amplified winter warming.

Physical-biological processes regulating summer sea-air CO2 exchanges along the Drake Passage and northern Antarctic Peninsula

Physical-biological processes regulating summer sea-air CO2 exchanges along the Drake Passage and northern Antarctic Peninsula

Environmental DNA as a novel tool for monitoring fish community structure and diversity feature in the northern Antarctic Peninsula

Environmental DNA as a novel tool for monitoring fish community structure and diversity feature in the northern Antarctic Peninsula

A New Perspective on Past Export Production in the Subantarctic South Pacific for the Last ∼1.4 Myr

AbstractAccurate reconstructions of export production in the Subantarctic Zone of the Southern Ocean are crucial for understanding the carbon cycle during Earth's past. However, due to the strong bottom water circulation of the Antarctic Circumpolar Current, sediment redistribution complicates age‐model‐derived bulk mass accumulation rates (BMAR). Here, we assess export production and its drivers over the past ∼1.4 Myr near the Drake Passage entrance using BMAR of biogenic barium, organic carbon, biogenic opal, calcium carbonate, and iron from sediment core PS97/093‐2, all of which are corrected for lateral sediment redistribution (corr‐BMAR). To quantify this correction, we explore the relationship between sortable silt as a bottom current strength proxy and 230Th‐derived focusing factors as indicators of lateral redistribution of sediments, respectively. Our findings highlight peak Fe input prior and during glacials of the Mid‐Pleistocene Transition (MPT), likely driven by enhanced Patagonian weathering. The carbonate record indicates increased deep‐ocean corrosivity after around 1 Ma ago and displays a shift in the accumulation pattern post‐MPT, with only isolated peaks in some peak interglacials. The high carbonate values during MIS 11 likely relate to Gephyrocapsa coccolithophore propagation, preceded and followed by prolonged carbonate dissolution periods, possibly linked to the Mid‐Brunhes Event. After the MPT, productivity proxies respond to glacial and interglacial intensity, with maxima found during MIS 16, MIS 11, MIS 5, and the Holocene, while minima occur during MIS 15–12. Our findings offer insights into long‐term productivity dynamics and their relationship to important climatic events over the past 1.4 Myr.

Developing a palaeoceanographic proxy based on the dimensions of Adercotryma glomeratum: a case study in Drake Passage region (Antarctic Peninsula)

Developing a palaeoceanographic proxy based on the dimensions of Adercotryma glomeratum: a case study in Drake Passage region (Antarctic Peninsula)

Chaotic oceanic excitation of low-frequency polar motion variability

Abstract. Studies of Earth rotation variations generally assume that changes in non-tidal oceanic angular momentum (OAM) manifest the ocean's direct response to atmospheric forces. However, fluctuations in OAM may also arise from chaotic intrinsic ocean processes that originate in local nonlinear (e.g., mesoscale) dynamics and can map into motions and mass variations at basin scales. To examine whether such random mass redistributions effectively excite polar motion, we compute monthly OAM anomalies from a 50-member ensemble of eddy-permitting global ocean/sea ice simulations that sample intrinsic variability through a perturbation approach on model initial conditions. The resulting OAM (i.e., excitation) functions, χ^O, are examined for their spread, spectral content, and role in the polar motion excitation budget from 1995 to 2015. We find that intrinsic χ^O signals are comparable in magnitude to the forced component at all resolved periods except the seasonal band, amounting to ∼ 46 % of the total oceanic excitation (in terms of standard deviation) on interannual timescales. More than half of the variance in the intrinsic mass term contribution to χ^O is associated with a single global mode of random bottom pressure variability, likely generated by nonlinear dynamics in the Drake Passage. Comparisons of observed interannual polar motion excitation against the sum of known surficial mass redistribution effects are sensitive to the representation of intrinsic χ^O signals: reductions in the observed excitation variance can be as high as 68 % or as low as 50 % depending on the choice of the ensemble member. Chaotic oceanic excitation thus emerges as a new factor to consider when interpreting low-frequency polar motion changes in terms of core–mantle interactions or employing forward-modeled OAM estimates for Earth rotation predictions.

The Mono Lake and Laschamps Geomagnetic Excursions Recorded by Sediments in the Drake Passage

AbstractThe Drake Passage is characterized by strong ocean currents barely allowing the deposition of fine grained sediments. Only in smaller basins protected from these currents sediments are able to settle more or less continuously. Two sediment cores from within the Drake Passage were subjected to magnetostratigraphic analyses. In one core inclinations are too steep while they are too shallow in the other one. Tentatively, directions of both cores were slightly tilted so that the maximum of the inclination distribution aligns with the direction of a geocentric axial dipole. Inclination variations then correlate fairly well, while declinations still show only little congruence. This is interpreted as the result of locally varying bottom currents partly biasing the remanence acquisition processes. Nevertheless, due to the high latitude of the coring site at 58°S, the field vector is mostly dominated by inclination and intensity variations. Directional variations during the documented Mono Lake (34.5 ka) and Laschamps (41.0 ka) geomagnetic excursions are only slightly changed by the applied tilt‐correction and afterward correlate very well from core to core. The Mono Lake excursion is characterized by shallow inclinations only, indicating a non‐axial dipolar field geometry. The field vector during the Laschamps excursion reaches a fully reversed direction. Both excursions are associated with clear minima in paleointensity. During the Laschamps excursion even a slight field recovery can be observed during the reversed phase of the field vector. Both excursions in Drake Passage sediments are terminated fairly abruptly followed by a more or less steep increase in paleointensity.

Stepwise Oligocene–Miocene breakdown of subpolar gyres and strengthening of the Antarctic Circumpolar Current

Abstract. Through the Cenozoic (66–0 Ma), the dominant mode of ocean surface circulation in the Southern Ocean transitioned from two large subpolar gyres to circumpolar circulation with a strong Antarctic Circumpolar Current (ACC) and complex ocean frontal system. Recent investigations in the southern Indian and Pacific oceans show warm Oligocene surface water conditions with weak frontal systems that started to strengthen and migrate northwards during the late Oligocene. However, due to the paucity of sedimentary records and regional challenges with traditional proxy methods, questions remain about the southern Atlantic oceanographic transition from gyral to circumpolar circulation, with associated development of frontal systems and sea ice cover in the Weddell Sea. Our ability to reconstruct past Southern Ocean surface circulation and the dynamic latitudinal positions of the frontal systems has improved over the past decade. Specifically, increased understanding of the modern ecologic affinity of organic-walled dinoflagellate cyst (dinocyst) assemblages from the Southern Ocean has improved reconstructions of distinct past oceanographic conditions (sea surface temperature, salinity, nutrients, and sea ice) using downcore assemblages from marine sediment records. Here we present new late Oligocene to latest Miocene (∼ 26–5 Ma) dinocyst assemblage data from marine sediment cores in the southwestern Atlantic Ocean (International Ocean Discovery Program (IODP) Site U1536, Ocean Drilling Program (ODP) Site 696 and piston cores from Maurice Ewing Bank). We compare these to previously published latest Eocene–latest Miocene (∼ 37–5 Ma) dinocyst assemblage records and sea surface temperature (SST) reconstructions available from the SW Atlantic Ocean in order to reveal oceanographic changes as the Southern Ocean gateways widen and deepen. The observed dinocyst assemblage changes across the latitudes suggest a progressive retraction of the subpolar gyre and southward migration of the subtropical gyre in the Oligocene–early Miocene, with strengthening of frontal systems and progressive cooling since the middle Miocene (∼ 14 Ma). Our data are in line with the timing of the removal of bathymetric and geographic obstructions in the Drake Passage and Tasmanian Gateway regions, which enhanced deep-water throughflow that broke down gyral circulation into the Antarctic circumpolar flow. Although the geographic and temporal coverage of the data is relatively limited, they provide a first insight into the surface oceanographic evolution of the late Cenozoic southern Atlantic Ocean.

The Effect of Southern Ocean Topography on the Global MOC and Abyssal Water Mass Distribution

Abstract We investigate the role of Southern Ocean topography and wind stress in the deep and abyssal ocean overturning and water mass composition using a suite of idealized global ocean circulation models. Specifically, we address how the presence of a meridional ridge in the vicinity of Drake Passage and the formation of an associated Southern Ocean gyre influence the water mass composition of the abyssal cell. Our experiments are carried out using a numerical representation of the global ocean circulation in an idealized two-basin geometry under varying wind stress and Drake Passage ridge height. In the presence of a low Drake Passage ridge, the overall strength of the meridional overturning circulation is primarily influenced by wind stress, with a topographically induced weakening of the middepth cell and concurrent strengthening of the abyssal cell occurring only after ridge height passes 2500 m. Passive tracer experiments show that a strengthening middepth cell leads to increased abyssal ventilation by North Atlantic water masses, as more North Atlantic Deep Water (NADW) enters the Southern Ocean and then spreads into the Indo-Pacific. We repeat our tracer experiments without restoring in the high-latitude Southern Ocean in order to identify the origin of water masses that circulate through the Southern Ocean before sinking into the abyss as Antarctic Bottom Water. Our results from these “exchange” tracer experiments show that an increasing ridge height in Drake Passage and the concurrent gyre spinup lead to substantially decreased NADW-origin waters in the abyssal ocean, as more surface waters from north of the Antarctic Circumpolar Current (ACC) are transferred into the Antarctic Bottom Water formation region. Significance Statement The objective of this study is to investigate how topographic features in the Southern Ocean can affect the overall structure of Earth’s large-scale ocean circulation and the distribution of water masses in the abyssal ocean. We focus on the Southern Ocean because the region is of central importance for exchange between the Atlantic and Indo-Pacific Ocean basins and for CO2 and heat uptake into the abyssal ocean. Our results indicate that Southern Ocean topography plays a major role in the overall circulation by 1) controlling the direct transfer of abyssal waters from the Atlantic to the Indo-Pacific via its influence on the Atlantic meridional overturning circulation and 2) controlling the coupling between the abyssal ocean and surface waters north of the Antarctic Circumpolar Current via the Southern Ocean gyre.

Seawater Lead Isotopes Record Early Miocene to Modern Circulation Dynamics in the Pacific Sector of the Southern Ocean

AbstractThe Antarctic Circumpolar Current (ACC) is Earth's largest current flowing around Antarctica at all depths and connecting major ocean basins, thus representing an important component of Earth's climate. However, the timing and key controls determining ACC flow path and its strength as a function of past climatic boundary conditions that ultimately resulted in its modern configuration remain unclear due to major uncertainties in paleoceanographic and tectonic reconstructions. Here we present a unique high‐resolution laser ablation‐derived late Cenozoic seawater lead isotope record obtained from a hydrogenetic ferromanganese crust from the Pacific sector of the Southern Ocean. Our Pb isotope data reveal that the ACC has experienced five stable circulation states since the early Miocene which were separated by four major transitions observed at 17.5‐14.6, 12, 10 and 5 Ma. We suggest that the relatively abrupt transitions between ACC circulation state were mainly induced by tectonic changes, whereas the impact of climatic changes was of secondary importance. According to our data the modern ACC configuration formed 5 million years ago, likely in response to the closure of the Panama Seaway. Since the Drake Passage (DP) has already been an open seaway since at least the late Miocene, our results demonstrate that DP opening was not the only factor affecting past ACC circulation. Our data also show that changes in the latitudinal position of the ACC were linked to the middle Miocene waxing and waning of the Antarctic ice sheets, which emphasizes the ACC's critical role as a key control of Antarctic glaciation.

Phylogeography of Cold Water Soft Coral Alcyonium spp. (Anthozoa, Octocorallia: Alcyonacea) Between South America and the West Antarctic Peninsula.

The Antarctic marine environment has a unique geologic and climatic history that has contributed to the evolution of high species diversity. Given the current trend of environmental warming, understanding the history of Antarctic species is crucial for predicting the impact of climate change on ecosystem function. Soft corals are a group of striking presence in the benthic marine assemblages in the Southern Ocean, which is recognized as a biodiversity hotspot. DNA sequences (Cox1, mtMutS, and 28S rDNA) were utilized for molecular phylogenetic reconstructions, species delimitations, and divergence estimations to investigate the spatial patterns of genetic diversity in Alcyonium species in the southern South American-Antarctic region. Significant genetic divergence was observed between regions, with a clear genetic break between South America and the West Antarctic Peninsula and the identification of four putative species. Divergence time estimates indicated that Alcyonium's diversification began about 41.1 million years ago (Ma), coinciding with the opening of the Drake Passage and the formation of the Antarctic Circumpolar Current (ACC, ~42 Ma). This indicates that Alcyonium has persisted insitu for an extensive period, enduring a wide range of environmental conditions.

Orbital timescale CaCO3 burial and dissolution changes off the Chilean margin in the subantarctic Pacific over the past 140 kyr

Calcium carbonate (CaCO3) dissolution at the Southern Ocean seafloor has hypothetically contributed to lowering the atmospheric carbon dioxide concentration by increasing ocean alkalinity during glacial periods. We present new CaCO3 burial and dissolution records from two sediment cores obtained off the Chilean margin in the subantarctic SE Pacific and covering the past 140 kyr since Marine Isotope Stage (MIS) 6. These records include CaCO3 contents and mass accumulation rates, and microfossil-based analysis results, including fragmentation ratios, sieve-based weights (SBWs), and ultrastructural observations of planktic foraminiferal tests. Our bulk CaCO3-based analyses and Globorotalia inflata SBWs revealed three major CaCO3 dissolution events during colder stages of MIS 5d and 5b and at the MIS 5/4 boundary that are traceable events in the eastern South Pacific along the Chilean margin and in the Drake Passage. Furthermore, CaCO3 burial exhibited pronounced glacial/interglacial fluctuations, with almost no burial during glacials (MIS 6, 4, 3, and 2) and recovery during interglacials (MIS 5e and 1) and early glacials (MIS 5d–a). This pattern agrees with previous observations over a wide area of the Southern Ocean, except in the deep Cape Basin > 4600 m in the South Atlantic Ocean. Considering that our sites were located upstream of the Drake Passage, the Circumpolar Deep Water, which was influenced by carbon-rich Pacific Deep Water, likely propagated from the subantarctic eastern Pacific to the South Atlantic at least at depths of ~ 3000 to ~ 4000 m and decreased CaCO3 burial during glacials. These findings supported the importance of carbonate compensation in the Southern Ocean for the carbon cycle on the glacial/interglacial timescale.

Eocene Shark Teeth From Peninsular Antarctica: Windows to Habitat Use and Paleoceanography

AbstractEocene climate cooling, driven by the falling pCO2 and tectonic changes in the Southern Ocean, impacted marine ecosystems. Sharks in high‐latitude oceans, sensitive to these changes, offer insights into both environmental shifts and biological responses, yet few paleoecological studies exist. The Middle‐to‐Late Eocene units on Seymour Island, Antarctica, provide a rich, diverse fossil record, including sharks. We analyzed the oxygen isotope composition of phosphate from shark tooth bioapatite (δ18Op) and compared our results to co‐occurring bivalves and predictions from an isotope‐enabled global climate model to investigate habitat use and environmental conditions. Bulk δ18Op values (mean 22.0 ± 1.3‰) show no significant changes through the Eocene. Furthermore, the variation in bulk δ18Op values often exceeds that in simulated seasonal and regional values. Pelagic and benthic sharks exhibit similar δ18Op values across units but are offset relative to bivalve and modeled values. Some taxa suggest movements into warmer or more brackish waters (e.g., Striatolamia, Carcharias) or deeper, colder waters (e.g., Pristiophorus). Taxa like Raja and Squalus display no shift, tracking local conditions in Seymour Island. The lack of difference in δ18Op values between pelagic and benthic sharks in the Late Eocene could suggest a poorly stratified water column, inconsistent with a fully opened Drake Passage. Our findings demonstrate that shark tooth bioapatite tracks the preferred habitat conditions for individual taxa rather than recording environmental conditions where they are found. A lack of secular variation in δ18Op values says more about species ecology than the absence of regional or global environmental changes.

Uncovering the oxic-suboxic microenvironment change in seamount flank through authigenic clay minerals in basaltic substrate of ferromanganese crust, Magellan seamount

In low-temperature ocean environments, basalt alteration by seawater precipitates authigenic clay minerals that serve as proxies for reconstructing paleo-ocean conditions because they reflect surrounding oxic-suboxic conditions. In this study, alteration rims on basaltic substrate associated with ferromanganese (Fe-Mn) crust from the Magellan seamount KC-7 were identified by microscopic analyses. Mineralogical and geochemical analyses indicate that the alteration rims contain K-enriched Fe-smectite and glauconite which suggest that seawater-basalt interaction occurred under oxic conditions and in the presence of organic-rich suboxic conditions, respectively. These disparate environmental conditions suggest that the environment changed before and after Fe-Mn crusts formed. During the Cenozoic hyperthermal events, oxygen-rich bottom water was supplied by upwelling driven by the geomorphological influence of the seamounts, which may have led to basalt alteration. The K-enriched Fe-smectites, which indicate oxic condition, formed via seawater-basalt interactions before the Fe-Mn crust incrustation. Later, during the Eocene, the opening of the Drake Passage enhanced the supply of oxygen-rich seawater to the Magellan Seamounts, thereby enabling the formation of hydrogenetic Fe-Mn crust. After the incrustation of seamount flanks with Fe-Mn crusts, the carbonate fluorapatite (CFA), a product of the global phosphatization event, filled the pores in the Fe-Mn crusts during Oi-1 glaciation. As a result, seawater-basalt interactions decreased and led to suboxic conditions, in which glauconite formed as organic matter was remineralized under the organic-rich conditions in the basaltic substrate. This authigenic clay mineral formation sequence suggests that changes in ocean circulation and subsequent changes in the oxic-suboxic conditions in the basaltic substrate occurred on the western Pacific seamount KC-7.

Oceanographic features boost latitudinal patterns in copepod body size distribution in the South Atlantic

AbstractThe South Atlantic Ocean (SAO) is an under‐sampled ocean where the influence of environmental drivers on copepod body size is poorly understood. This study investigated the body size distribution of copepods from 13°S to 64°S to test Bergmann's rule, which predicts the occurrence of smaller organisms in warmer areas. We hypothesized that additional influence of oceanographic features strengthens this pattern. Zooplankton were sampled during the austral summer from the chlorophyll maximum depth up to the surface, at approximately 100 m depth, using a 200‐μm net. The samples were analyzed using the ZooScan imaging system and were classified using the Ecotaxa tool. We estimated copepod family abundance, biomass, and size structure, and their relationships with environmental variables were assessed through generalized linear mixed models (GLMM). Although most copepods increased in size at higher latitudes, not all families followed Bergmann's rule. Small adults of Clausocalanidae, Paracalanidae, Corycaeidae, and Oncaeidae contributed mostly in the Brazil Current (BC), while Calanidae copepodites disproportionately contributed to overall biomass, and Oithonidae adults were the most abundant in high latitudes. Copepod abundance or biomass hotspots were present in the southern limit of the warm BC, at the Subtropical Confluence Zone, and in the subantarctic waters at the Drake passage. Our results suggest that oceanographic features strengthen latitudinal body size relationships due to food availability, and the importance of different life history strategies.

Spatial and temporal variability of the freezing level in Patagonia's atmosphere

Abstract. The height of the 0 °C isotherm (H0), which commonly signals the freezing level, denotes the lowest altitude within the atmosphere where the air temperature reaches 0 °C. This can be used as an indicator of the transition between rain and snow, making it useful for monitoring and visualizing the height of freezing temperatures in the atmosphere. We study the spatial and temporal variability of H0 across Patagonia (41–54° S) for the 1959–2021 period using reanalysis data from ERA5. Our results indicate that the average isotherm in Patagonia is 1691 m above sea level (m a.s.l.). The spatial distribution of the annual mean field highlights the contrast in the region, with an average maximum of 2658 m a.s.l. in the north and minimum of 913 m a.s.l. in the south. Regarding seasonal variability in the region, H0 ranges from 575 m a.s.l. (winter) to 3346 m a.s.l. (summer). Further, the significant trends calculated over the period show positive values in the whole area. This indicates an upward annual trend in the H0, between 8.8 and 36.5 m per decade from 1959–2021, with the higher value observed in northwestern Patagonia. These upward trends are stronger during summer (8–61 m per decade). Empirical orthogonal function (EOF) analysis was performed on H0 anomalies. The first EOF mode of H0 variability accounts for 84 % of the total variance, depicting a monopole structure centred in the northwestern area. This mode exhibits a strong and significant correlation with the spatial average H0 anomaly field (r=0.85), the Southern Annular Mode (SAM; r= 0.58), temperature at 850 hPa in the Drake Passage (r=0.56), and sea surface temperature off the western coast of Patagonia (r=0.66), underscoring the significant role of these factors in influencing the vertical temperature profile within the region. The spatial distribution of the second (8 %) and third (4.4 %) EOF modes depicts a dipole pattern, offering additional insights into the processes influencing the 0 °C isotherm, especially on the western slope of Patagonia.