Paleogene Polar Plankton and export productivity changes between the Eocene and Oligocene

2020 ◽  
Author(s):  
Gabrielle Rodrigues de Faria ◽  
David Lazarus ◽  
Ulrich Struck ◽  
Gayane Asatryan ◽  
Johan Renaudie ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Carbon Isotope ◽  
Ocean Circulation ◽  
Deep Sea ◽  
Fine Fraction ◽  
Weddell Sea ◽  
Oxygen And Carbon Isotope ◽  
The Antarctic ◽  
The Impact ◽  
Export Productivity

<p>Aiming to support the prediction of future climate developments, this project investigates the role on geological timescale of the ocean plankton in reducing atmospheric carbon concentration by exporting carbon to the deep-sea. While it is well-known that the transition from the Eocene to the Oligocene brought significant climate changes and, in connection, also a change of the oceans’ carbon export production, the important role of phytoplankton and the links to changing ocean circulation are still poorly understood, as is, similarly, the impact on those changes on the diversity of the plankton contributing to the carbon pump. Investigating the nature of this interaction will provide significant insight into the functions of the oceans as climate regulators.</p><p>To address those question, we are generating diversity and absolute abundance data for diatoms and radiolarians, biogeographic data for radiolarians, as well as oxygen and carbon isotope data on planktic and benthic foraminifera, and on the fine fraction (<45µm, i. e. coccoliths), as well as other proxies to estimate surface and deep ocean temperatures and export productivity. These will be generated as paired data from individual samples in various deep-sea drilling sites in and around the Southern Ocean (as it is the focal point of the climatic/oceanographic changes at that period). These data will then be compiled and confronted to an ocean circulation model.</p><p>Here we will present our results so far (oxygen and carbon isotope on the bulk fine fraction, as well as radiolarian and diatom diversity estimates), based on two main localities from the antarctic (ODP Site 689B from the Weddell Sea) and the subantarctic (ODP Site 1090B on the southern flank of the Agulhas ridge) South Atlantic. A comparison with a newly generated, database-driven diversity analysis of the same groups in the same region, using the Neptune (NSB) database, will also be shown. While the exhaustive taxonomical compilation made on these two sites for the diatoms records three times more species than what was recorded in the literature for the Southern Ocean biome, it still shows an evolutionary turnover at the Eocene-Oligocene, just as the classic, NSB-driven analysis does. The fine fraction oxygen isotope at both sites 689B and 1090B show a pattern similar to that recorded in planktonic foraminifera in neighbour sites, indicating a significant drop in SST close to the Eocene-Oligocene boundary, while the fine fraction carbon isotope signal in the antarctic site shows a subsequent decrease indicating changes in exported productivity 2Myr after the global cooling.</p>

Bathymetric control of subpolar gyres and the overturning circulation in the Southern Ocean

2021 ◽  
Author(s):  
Andrew L. Stewart ◽  
Shantong Sun
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Weddell Sea ◽  
Subpolar Gyre ◽  
Buoyancy Forcing ◽  
Regional Circulation ◽  
Submarine Ridge ◽  
Horizontal Circulation ◽  
Circumpolar Current ◽  
The Antarctic

Abstract The subpolar gyres of the Southern Ocean form an important dynamical link between the Antarctic Circumpolar Current (ACC) and the coastline of Antarctica. Despite their key involvement in the production and export of bottom water and the poleward transport of oceanic heat, these gyres are rarely acknowledged in conceptual models of the Southern Ocean circulation, which tend to focus on the zonally-averaged overturning across the ACC. To isolate the effect of these gyres on the regional circulation, we carried out a set of numerical simulations with idealized representations of the Weddell Sea sector in the Southern Ocean. A key result is that the zonally-oriented submarine ridge along the northern periphery of the subpolar gyre plays a fundamental role in setting the stratification and circulation across the entire region. In addition to sharpening and strengthening the horizontal circulation of the gyre, the zonal ridge establishes a strong meridional density front that separates the weakly stratified subpolar gyre from the more stratified circumpolar flow. Critically, the formation of this front shifts the latitudinal outcrop position of certain deep isopycnals such that they experience different buoyancy forcing at the surface. Additionally, the zonal ridge modifies the mechanisms by which heat is transported poleward by the ocean, favoring heat transport by transient eddies while suppressing that by stationary eddies. This study highlights the need to characterize how bathymetry at the subpolar gyre-ACC boundary may constrain the transient response of the regional circulation to changes in surface forcing.

Cooling of the Northern Hemisphere triggered by Northeast Atlantic opening at the Eocene – Oligocene Transition 

2021 ◽  
Author(s):  
Eivind Straume ◽  
Aleksi Nummelin ◽  
Carmen Gaina ◽  
Kerim Nisancioglu
Keyword(s):  
Southern Ocean ◽  
Northern Hemisphere ◽  
Ocean Circulation ◽  
The Arctic ◽  
The North ◽  
Dynamic Support ◽  
Climate Transition ◽  
Iceland Plume ◽  
The Antarctic ◽  
The Impact

<p>The Eocene – Oligocene Transition (~33.7 million years ago), marks the largest step transformation within the Cenozoic cooling trend, and is characterized by a sudden growth of the Antarctic ice sheets. The role of changes in oceanic basin configuration and the evolution of key oceanic gateways in triggering these climatic variations remains disputed. Here we implement a new state-of-the-art paleogeography model in the Norwegian Earth System Model (NorESM-F) to investigate the effect of oceanic gateway changes on the Eocene – Oligocene climate. We run different cases using realistic max/min depth configurations of the Atlantic – Arctic oceanic gateways, the Tethys Seaway, and the Southern Ocean gateways, and investigate the ocean and climate sensitivity to these changes. In addition, we run separate simulations investigating the impact on the carbon cycle. The models show that changes in the Atlantic – Arctic gateways (i.e. Greenland – Scotland Ridge and the Fram Strait) cause the most significant changes in ocean circulation and climate compared to the Southern Ocean gateways or the Tehthys Seaway. The Iceland mantle plume caused depth variations on the Greenland – Scotland Ridge at this time, and our model result indicate that variations in dynamic support from the Iceland plume could have played a key role in the Eocene – Oligocene climate transition. Essentially, reduced dynamic support from the plume deepen the Greenland – Scotland Ridge and cause freshwater leakage from the Arctic Ocean which inhibits deep water formation in the North Atlantic, reducing the AMOC and ultimately cool the Northern Hemisphere.</p>

On the impact of sea ice in a global ocean circulation model

1997 ◽  
Vol 25 ◽  
pp. 111-115 ◽  
Author(s):  
Achim Stössel
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Deep Ocean ◽  
Global Ocean ◽  
Convective Activity ◽  
The Impact

This paper investigates the long-term impact of sea ice on global climate using a global sea-ice–ocean general circulation model (OGCM). The sea-ice component involves state-of-the-art dynamics; the ocean component consists of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the physical description of sea ice, significant changes are detected in the convective activity, in the hydrographic properties and in the thermohaline circulation of the ocean model. Most of these changes originate in the Southern Ocean, emphasizing the crucial role of sea ice in this marginally stably stratified region of the world's oceans. Specifically, if the effect of brine release is neglected, the deep layers of the Southern Ocean warm up considerably; this is associated with a weakening of the Southern Hemisphere overturning cell. The removal of the commonly used “salinity enhancement” leads to a similar effect. The deep-ocean salinity is almost unaffected in both experiments. Introducing explicit new-ice thickness growth in partially ice-covered gridcells leads to a substantial increase in convective activity, especially in the Southern Ocean, with a concomitant significant cooling and salinification of the deep ocean. Possible mechanisms for the resulting interactions between sea-ice processes and deep-ocean characteristics are suggested.

An Antarctic shelf population of the deep-sea, Pacific brachiopod Neorhynchia strebeli

1997 ◽  
Vol 77 (2) ◽  
pp. 399-407 ◽  
Author(s):  
David K.A. Barnes ◽  
Lloyd S. Peck
Keyword(s):  
Deep Sea ◽  
Growth Function ◽  
Weddell Sea ◽  
Von Bertalanffy ◽  
Growth Rings ◽  
Von Bertalanffy Growth Function ◽  
Annual Periodicity ◽  
A Site ◽  
The Antarctic ◽  
Order Rhynchonellida

Thirty-five specimens of the articulate brachiopod Neorhynchia strebeli were collected from a site at 814 m in the Weddell Sea. This was only the second species of the order Rhynchonellida to be found in Antarctica. Formerly N. strebeli was known solely from abyssal Pacific Ocean localities. A circumantarctic distribution is suggested in addition to the known deep-sea Pacific range. The specimens of this collection showed considerable commissure variation, suggesting that the previously proposed erection of two subspecies on the basis of this character is erroneous, and emphasises the phenotypic plasticity of some articulate brachiopods. The valve lengths and the number of alpha growth rings in the sample showed a normal distribution and a von Bertalanffy growth function was fitted to the data: Lt = 23 (1-exp[-0·228t]). If the alpha growth rings were of annual periodicity, the ages attained by the Antarctic N. strebeli of 11 y would be substantially lower than those reported for other Weddell Sea brachiopods. The epibiotic communities occurring on the valves of N. strebeli were impoverished, which is characteristic of deep water Antarctic brachiopods. The few specimens collected with their substratum were attached to small pebbles, but the typical attachment substrata may be different.

Molecular systematics of Thouarella (Octocorallia:Primnoidae) with the description of three new species from the Southern Ocean based on combined molecular and morphological evidence

2021 ◽  
Author(s):  
Mónica Núñez-Flores ◽  
Daniel Gomez-Uchida ◽  
Pablo J. López-González
Keyword(s):  
New Species ◽  
Southern Ocean ◽  
Species Delimitation ◽  
Nuclear Dna ◽  
Phylogenetic Analyses ◽  
Weddell Sea ◽  
Morphological Evidence ◽  
Three New Species ◽  
Taxonomic Framework ◽  
The Antarctic

Thouarella Gray, 1870, is one of the most speciose genera among gorgonians of the family Primnoidae (Cnidaria:Octocorallia:Anthozoa), being remarkably diverse in the Antarctic and sub-Antarctic seafloor. However, their diversity in the Southern Ocean is likely underestimated. Phylogenetic analyses of mitochondrial and nuclear DNA markers were integrated with species delimitation approaches as well as morphological colonial and polyps features and skeletal SEM examinations to describe and illustrate three new species within Thouarella, from the Weddell Sea, Southern Ocean: T. amundseni sp. nov., T. dolichoespinosa sp. nov. and T. pseudoislai sp. nov. Our species delimitation results suggest, for the first time, the potential presence of Antarctic and sub-Antarctic cryptic species of primnoids, based on the likely presence of sibling species within T. undulata and T. crenelata. With the three new species here described, the global diversity of Thouarella has increased to 41 species, 15 of which are endemic to the Antarctic and sub-Antarctic waters. Consequently, our results provide new steps for uncovering the shelf benthonic macrofauna’s hidden diversity in the Southern Ocean. Finally, we recommend using an integrative taxonomic framework in this group of organisms and species delimitation approaches because the distinctions between some Thouarella species based only on a superficial examination of their macro- and micromorphological features is, in many cases, limited.

Last Glacial Maximum Antarctic sea ice linked with global mean ocean temperature: evidence from PMIP3, PMIP4 and MIROC-4m simulations

2021 ◽  
Author(s):  
Tristan Vadsaria ◽  
Sam Sherriff-Tadano ◽  
Ayako Abe-Ouchi ◽  
Takashi Obase ◽  
Wing-Le Chan ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Last Glacial Maximum ◽  
Ocean Circulation ◽  
Glacial Maximum ◽  
Ocean Temperature ◽  
Sea Ice Extent ◽  
Last Glacial ◽  
Antarctic Sea Ice ◽  
The Antarctic

<p>Southern Ocean sea ice and oceanic fronts are known to play an important role on the climate system, carbon cycles, bottom ocean circulation, and Antarctic ice sheet. However, many models of the previous Past-climate Model Intercomparison Project (PMIP) underestimated sea-ice extent (SIE) for the Last Glacial Maximum (LGM)(Roche et al., 2012; Marzocchi and Jensen, 2017), mainly because of surface bias (Flato et al., 2013) that may have an impact on mean ocean temperature (MOT). Indeed, recent studies further suggest an important link between Southern Ocean sea ice and mean ocean temperature (Ferrari et al., 2014; Bereiter et al., 2018 among others). Misrepresent the Antarctic sea-ice extent could highly impact deep ocean circulation, the heat transport and thus the MOT. In this study, we will stress the relationship between the distribution of Antarctic sea-ice extent and the MOT through the analysis of the PMIP3 and PMIP4 exercise and by using a set of MIROC models. To date, the latest version of MIROC improve its representation of the LGM Antarctic sea-ice extent, affecting the deep circulation and the MOT distribution (Sherriff-Tadano et al., under review).</p><p>Our results show that available PMIP4 models have an overall improvement in term of LGM sea-ice extent compared to PMIP3, associated to colder deep and bottom ocean temperature. Focusing on MIROC (4m) models, we show that models accounting for Southern Ocean sea-surface temperature (SST) bias correction reproduce an Antarctic sea-ice extent, 2D-distribution, and seasonal amplitude in good agreement with proxy-based data. Finally, using PMIP-MIROC analyze, we show that it exists a relationship between the maximum SIE and the MOT, modulated by the Antarctic intermediate and bottom waters.</p>

The Southern Ocean and its interaction with the Antarctic Ice Sheet

Science ◽  
2020 ◽  
Vol 367 (6484) ◽  
pp. 1326-1330
Author(s):  
David M. Holland ◽  
Keith W. Nicholls ◽  
Aurora Basinski
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Thermal Structure ◽  
Ice Sheet ◽  
Major Influence ◽  
Antarctic Ice Sheet ◽  
Ice Shelves ◽  
Air Temperatures ◽  
The Antarctic ◽  
Circulation Changes

The Southern Ocean exerts a major influence on the mass balance of the Antarctic Ice Sheet, either indirectly, by its influence on air temperatures and winds, or directly, mostly through its effects on ice shelves. How much melting the ocean causes depends on the temperature of the water, which in turn is controlled by the combination of the thermal structure of the surrounding ocean and local ocean circulation, which in turn is determined largely by winds and bathymetry. As climate warms and atmospheric circulation changes, there will be follow-on changes in the ocean circulation and temperature. These consequences will affect the pace of mass loss of the Antarctic Ice Sheet.

Benthic hydroids (Cnidaria, Hydrozoa) from the Weddell Sea (Antarctica)

Zootaxa ◽  
2019 ◽  
Vol 4570 (1) ◽  
pp. 1
Author(s):  
JOAN J. SOTO ÀNGEL ◽  
ÁLVARO L. PEÑA CANTERO
Keyword(s):  
Southern Ocean ◽  
New Records ◽  
Weddell Sea ◽  
Reproductive Phenology ◽  
Antarctic Region ◽  
Bathymetric Range ◽  
Eastern Sector ◽  
Number Of Species ◽  
The Antarctic

Hydrozoans are a conspicuous component of Antarctic benthic communitites. Recent taxonomic effort has led to a substantial increase in knowledge on the diversity of benthic hydroids from some areas of the Southern Ocean, including the Weddell Sea, the largest sea in the Antarctic region. However, the study of many hydrozoan taxa are still pending, and the diversity in this huge region is expected to be higher than currently known. In order to contribute to the knowledge of taxonomy, ecology and distribution of these cnidarians, a study of unpublished material collected by several German Antarctic expeditions aboard the RV Polarstern in the eastern sector of the Weddell Sea has been conducted. A total of 77 species belonging to 22 families and 28 genera of benthic hydroids have been inventoried, constituting the most prolific collection hitherto analyzed. Most species (81%) belong to Leptothecata, but the observed share of Anthoathecata (19%) is higher than in previous Antarctic hydrozoan studies. Symplectoscyphidae was the most speciose family with 16 representatives (22%), followed by Haleciidae with 10 (14%) and Staurothecidae with 8 (11%). The number of species known in the area was increased with 27 new records, including several species rarely documented. As a result, the Weddell Sea becomes the second Antarctic region in terms of hydrozoan diversity, with 89 species known to date. Novel data on the use of substrate, reproductive phenology, and bathymetric range are provided for the inventoried species. 

Acanthocopinae (Crustacea: Isopoda: Munnopsididae) from the Southern Ocean deep sea with the description of Acanthocope eleganta sp. nov.

Zootaxa ◽  
2004 ◽  
Vol 550 (1) ◽  
pp. 1 ◽  
Author(s):  
MARINA MALYUTINA ◽  
ANGELIKA BRANDT
Keyword(s):  
New Species ◽  
Southern Ocean ◽  
Deep Sea ◽  
Weddell Sea ◽  
Terminal Spine ◽  
Ventral Spine

Acanthocope eleganta sp. nov. is described from the abyssal Southern Ocean near the Southern Ocean Peninsula. The new species differs from others in the following: a slender dorsomedial spine on the pleon anteriorly, a pair of short dorsal spines and long ventral spine on each of pereonites 5 and 6; uropods half as long as the terminal spine of the pleotelson and with a minute exopod. A. annulatus Menzies, 1962 is redescribed; A. galatheae Wolff, 1962, previously known only from the Gulf of Panama and from Angola Basin, is recorded from the northwest Weddell Sea.

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