scholarly journals Surface-circulation change in the southwest Pacific Ocean across the Middle Eocene Climatic Optimum: inferences from dinoflagellate cysts and biomarker paleothermometry

2020 ◽  
Vol 16 (5) ◽  
pp. 1667-1689
Author(s):  
Margot J. Cramwinckel ◽  
Lineke Woelders ◽  
Emiel P. Huurdeman ◽  
Francien Peterse ◽  
Stephen J. Gallagher ◽  
...  
Keyword(s):  
Climate Change ◽  
Pacific Ocean ◽  
Southern Ocean ◽  
Ocean Circulation ◽  
Middle Eocene ◽  
Spatiotemporal Distribution ◽  
Ocean Currents ◽  
Surface Currents ◽  
Surface Ocean

Abstract. Global climate cooled from the early Eocene hothouse (∼52–50 Ma) to the latest Eocene (∼34 Ma). At the same time, the tectonic evolution of the Southern Ocean was characterized by the opening and deepening of circum-Antarctic gateways, which affected both surface- and deep-ocean circulation. The Tasmanian Gateway played a key role in regulating ocean throughflow between Australia and Antarctica. Southern Ocean surface currents through and around the Tasmanian Gateway have left recognizable tracers in the spatiotemporal distribution of plankton fossils, including organic-walled dinoflagellate cysts. This spatiotemporal distribution depends on both the physicochemical properties of the water masses and the path of surface-ocean currents. The extent to which climate and tectonics have influenced the distribution and composition of surface currents and thus fossil assemblages has, however, remained unclear. In particular, the contribution of climate change to oceanographic changes, superimposed on long-term and gradual changes induced by tectonics, is still poorly understood. To disentangle the effects of tectonism and climate in the southwest Pacific Ocean, we target a climatic deviation from the long-term Eocene cooling trend: the Middle Eocene Climatic Optimum (MECO; ∼40 Ma). This 500 kyr phase of global warming was unrelated to regional tectonism, and thus provides a test case to investigate the ocean's physicochemical response to climate change alone. We reconstruct changes in surface-water circulation and temperature in and around the Tasmanian Gateway during the MECO through new palynological and organic geochemical records from the central Tasmanian Gateway (Ocean Drilling Program Site 1170), the Otway Basin (southeastern Australia), and the Hampden Beach section (New Zealand). Our results confirm that dinocyst communities track specific surface-ocean currents, yet the variability within the communities can be driven by superimposed temperature change. Together with published results from the east of the Tasmanian Gateway, our new results suggest a shift in surface-ocean circulation during the peak of MECO warmth. Simultaneous with high sea-surface temperatures in the Tasmanian Gateway area, pollen assemblages indicate warm temperate rainforests with paratropical elements along the southeastern margin of Australia. Finally, based on new age constraints, we suggest that a regional southeast Australian transgression might have been coincident with the MECO.

scholarly journals Surface-circulation change in the Southern Ocean across the Middle Eocene Climatic Optimum: inferences from dinoflagellate cysts and biomarker paleothermometry

2019 ◽  
Author(s):  
Margot J. Cramwinckel ◽  
Lineke Woelders ◽  
Emiel P. Huurdeman ◽  
Francien Peterse ◽  
Stephen J. Gallagher ◽  
...  
Keyword(s):  
Climate Change ◽  
Southern Ocean ◽  
Ocean Circulation ◽  
Middle Eocene ◽  
Chemical Properties ◽  
Spatiotemporal Distribution ◽  
Surface Currents ◽  
Dinoflagellate Cysts ◽  
Physico Chemical ◽  
Climatic Optimum

Abstract. Global climate cooled from the early Eocene hothouse (~ 52–50 Ma) to the latest Eocene (~ 34 Ma). At the same time, the tectonic evolution of the Southern Ocean was characterized by the opening and deepening of circum-Antarctic gateways, which affected both surface- and deep-ocean circulation. The Tasman Gateway played a key role in regulating ocean throughflow between Australia and Antarctica. Southern Ocean surface currents through and around the Tasman Gateway have left recognizable tracers in the spatiotemporal distribution of plankton fossils, including organic-walled dinoflagellate cysts. This spatiotemporal distribution depends on physico-chemical properties of the water masses in which these organisms thrived. The degree to which the geographic path of surface currents (primarily controlled by tectonism) or their physico-chemical properties (significantly impacted by climate) have controlled the composition of the fossil assemblages has, however, remained unclear. In fact, it is yet poorly understood to what extent oceanographic response as a whole was dictated by climate change, independent of tectonics-induced oceanographic changes that operate on longer time scales. To disentangle the effects of tectonism and climate in the southwest Pacific Ocean, we target a climatic deviation from the long-term Eocene cooling trend, a 500 thousand year long global warming phase termed the Middle Eocene Climatic Optimum (MECO; ~ 40 Ma). The MECO warming is unrelated to regional tectonism, and thus provides a test case to investigate the oceans physiochemical response to climate change only. We reconstruct changes in surface-water circulation and temperature in and around the Tasman Gateway during the MECO through new palynological and organic geochemical records from the central Tasman Gateway (Ocean Drilling Program Site 1170), the Otway Basin (southeastern Australia) and the Hampden Section (New Zealand). Our results confirm that dinocyst communities track tectonically driven circulation patterns, yet the variability within these communities can be driven by superimposed temperature change. Together with published results from the east of the Tasman Gateway, our results suggest that as surface-ocean temperatures rose, the East Australian Current extended further southward during the peak of MECO warmth. Simultaneous with high sea-surface temperatures in the Tasman Gateway area, pollen assemblages indicate warm temperate rainforests with paratropical elements along the southeastern margin of Australia. Finally, based on new age constraints we suggest that a regional southeast Australian transgression might have been caused by sea-level rise during MECO.

scholarly journals <i>Brief communication</i> "The 2013 Erebus Glacier tongue calving event"

2013 ◽  
Vol 7 (2) ◽  
pp. 1749-1760
Author(s):  
C. L. Stevens ◽  
P. Sirguey ◽  
G. H. Leonard ◽  
T. G. Haskell
Keyword(s):  
Ocean Circulation ◽  
Ocean Currents ◽  
Mcmurdo Sound ◽  
Glacier Tongue ◽  
Surface Ocean ◽  
Fast Ice

Abstract. The Erebus Glacier Tongue, a~small floating glacier in southern McMurdo Sound, is one of the best-studied ice tongues in Antarctica. Despite this, its calving on the 27 February 2013 (UTC) was around 10 yr earlier than previously predicted. The calving was likely a result of ocean currents and the absence of fast ice. The subsequent trajectory of the newly-created iceberg supports previous descriptions of the surface ocean circulation in southern McMurdo Sound.

scholarly journals Early westward flow across the Tasman Gateway

2015 ◽  
Vol 11 (5) ◽  
pp. 5021-5048
Author(s):  
W. P. Sijp ◽  
A. S. von der Heydt ◽  
P. K. Bijl
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Surface Waters ◽  
Middle Eocene ◽  
Drake Passage ◽  
Easterly Wind ◽  
Wind Pattern ◽  
Sw Pacific ◽  
Field Evidence ◽  
Set Up

Abstract. The timing and role in ocean circulation and climate of the opening of Southern Ocean gateways is as yet elusive. Recent micropaleontological studies suggest the onset of throughflow of surface waters from the SW Pacific into the Australo-Antarctic Gulf through a southern shallow opening of the Tasman Gateway from 49–50 Ma onwards. Here, we present the first model results specific to the early-to-middle Eocene where, in agreement with the field evidence, southerly shallow opening of the Tasman Gateway indeed causes a westward flow across the Tasman Gateway. As a result, modelled estimates of dinoflagellate biogeography are in agreement with the recent findings. Crucially, in this situation where Australia is still situated far south and almost attached to Antarctica, the Drake Passage must be sufficiently restricted to allow the prevailing easterly wind pattern to set up this southerly restricted westward flow. In contrast, an open Drake Passage, to 517 m depth, leads to an eastward flow, even when the Tasman Gateway and the Australo-Antarctic gulf are entirely contained within the latitudes of easterly wind.

scholarly journals Anthropogenic carbon dynamics in the changing ocean

Ocean Science ◽  
2010 ◽  
Vol 6 (3) ◽  
pp. 605-614 ◽  
Author(s):  
J. F. Tjiputra ◽  
K. Assmann ◽  
C. Heinze
Keyword(s):  
Climate Change ◽  
Southern Ocean ◽  
High Latitude ◽  
Meridional Overturning Circulation ◽  
Future Climate Change ◽  
Carbon Uptake ◽  
Overturning Circulation ◽  
Anthropogenic Carbon ◽  
Natural Carbon

Abstract. The long-term response of CO2 fluxes to climate change at the ocean surface and within the ocean interior is investigated using a coupled climate-carbon cycle model. This study also presents the first attempt to quantify the evolution of lateral transport of anthropogenic carbon under future climate change. Additionally, its impact on regional carbon storage and uptake is also evaluated. For the 1850–2099 period, our climate change simulation predicts oceanic uptake of anthropogenic carbon of about 538±23 Pg C. Another simulation indicates that changes in physical climate and its associated biogeochemical feedbacks result in a release of natural carbon of about 22±30 Pg C. The natural carbon outgassing is attributed to the reduction in solubility and change in wind pattern in the Southern Hemisphere. After the anthropogenic carbon passes through the air-sea interface, it is predominantly transported along the large scale overturning circulation below the surface layer. The spatial variations in the transport patterns in turn influence the evolution of future regional carbon uptake. In the North Atlantic, a slow down in the Atlantic Meridional Overturning Circulation weakens the penetration strength of anthropogenic carbon into the deeper ocean, which leads to a reduced uptake rate in this region. In contrast, more than half of the anthropogenic carbon taken up in the high latitude Southern Ocean region (south of 58° S) is efficiently and continuously exported northward, predominantly into intermediate waters. This transport mechanism allows continuous increase in future carbon uptake in the high latitude Southern Ocean, where the annual uptake strength could reach 39.3±0.9 g C m−2 yr−1, more than twice the global mean of 16.0±0.3 g C m−2 yr−1 by the end of the 21st century. Our study further underlines the key role of the Southern Ocean in controlling long-term future carbon uptake.

Changes in the Antarctic sea ice ecosystem: potential effects on krill and baleen whales

2008 ◽  
Vol 59 (5) ◽  
pp. 361 ◽  
Author(s):  
Stephen Nicol ◽  
Anthony Worby ◽  
Rebecca Leaper
Keyword(s):  
Climate Change ◽  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
Trophic Levels ◽  
Global Ocean ◽  
Ecological Change ◽  
Cetacean Species ◽  
Baleen Whales ◽  
The Antarctic

The annual formation and loss of some 15 million km2 of sea ice around the Antarctic significantly affects global ocean circulation, particularly through the formation of dense bottom water. As one of the most profound seasonal changes on Earth, the formation and decay of sea ice plays a major role in climate processes. It is also likely to be impacted by climate change, potentially changing the productivity of the Antarctic region. The sea ice zone supports much wildlife, particularly large vertebrates such as seals, seabirds and whales, some exploited to near extinction. Cetacean species in the Southern Ocean will be directly impacted by changes in sea ice patterns as well as indirectly by changes in their principal prey, Antarctic krill, affected by modifications to their own environment through climate change. Understanding how climate change will affect species at all trophic levels in the Southern Ocean requires new approaches and integrated research programs. This review focuses on the current state of knowledge of the sea ice zone and examines the potential for climatic and ecological change in the region. In the context of changes already documented for seals and seabirds, it discusses potential effects on the most conspicuous vertebrate of the region, baleen whales.

scholarly journals Changes in the Subduction of Southern Ocean Water Masses at the End of the Twenty-First Century in Eight IPCC Models

2010 ◽  
Vol 23 (24) ◽  
pp. 6526-6541 ◽  
Author(s):  
Stephanie M. Downes ◽  
Nathaniel L. Bindoff ◽  
Stephen R. Rintoul
Keyword(s):  
Climate Change ◽  
Southern Ocean ◽  
Ocean Circulation ◽  
Comparison Method ◽  
Water Masses ◽  
Intermediate Water ◽  
Intergovernmental Panel ◽  
Mode Water ◽  
Surface Warming ◽  
Freshwater Fluxes

Abstract A multimodel comparison method is used to assess the sensitivity of Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) formation to climate change. For the Intergovernmental Panel on Climate Change A2 emissions scenario (where atmospheric CO2 is 860 ppm at 2100), the models show cooling and freshening on density surfaces less than about 27.4 kg m−3, a pattern that has been observed in the late twentieth century. SAMW (defined by the low potential vorticity layer) and AAIW (defined by the salinity minimum layer) warm and freshen as they shift to lighter density classes. Heat and freshwater fluxes at the ocean surface dominate the projected buoyancy gain at outcrop regions of SAMW and AAIW, whereas the net increase in the Ekman flux of heat and freshwater contributes to a lesser extent. This buoyancy gain, combined with shoaling of the winter mixed layer, reduces the volume of SAMW subducted into the ocean interior by a mean of 8 Sv (12%), and the subduction of AAIW decreases by a mean of 14 Sv (23%; 1 Sv ≡ 106 m3 s−1). Decreases in the projected subduction of the key Southern Ocean upper-water masses imply a slow down in the Southern Ocean circulation in the future, driven by surface warming and freshening. A reduction in the subduction of intermediate waters implies a likely future decrease in the capacity of the Southern Ocean to sequester CO2.

scholarly journals <i>Brief Communication</i> "The 2013 Erebus Glacier Tongue calving event"

2013 ◽  
Vol 7 (5) ◽  
pp. 1333-1337 ◽  
Author(s):  
C. L. Stevens ◽  
P. Sirguey ◽  
G. H. Leonard ◽  
T. G. Haskell
Keyword(s):  
Ocean Circulation ◽  
Ocean Currents ◽  
Mcmurdo Sound ◽  
Glacier Tongue ◽  
Surface Ocean ◽  
Fast Ice

Abstract. The Erebus Glacier Tongue, a small floating glacier in southern McMurdo Sound, is one of the best-studied ice tongues in Antarctica. Despite this, its calving on the 27 February 2013 (UTC) was around 10 yr earlier than previously predicted. The calving was likely a result of ocean currents and the absence of fast ice. The subsequent trajectory of the newly created iceberg supports previous descriptions of the surface ocean circulation in southern McMurdo Sound.

Response of the Pacific Ocean Circulation to Climate Change

2011 ◽  
Vol 49 (3) ◽  
pp. 235-244 ◽  
Author(s):  
Yiyong Luo ◽  
Lewis M. Rothstein
Keyword(s):  
Climate Change ◽  
Pacific Ocean ◽  
Ocean Circulation ◽  
The Pacific ◽  
The Pacific Ocean
Sign in / Sign up

Export Citation Format

Share Document