Southern Ocean Responses to a Warmer World

Southwest Pacific Ocean response to a warmer world – insights from Marine Isotope Stage 5e

Authors:

1. G. Cortese (a)
2. G. B. Dunbar (b)
3. L. Carter (b)
4. G. Scott (a)
5. H. Bostock (c)
6. M. Bowen (d)
7. M. Crundwell (a)
8. B. W. Hayward (e)
9. W. Howard (f)
10. J. I. Martínez (g)
11. A. Moy (h,i)
12. H. Neil (c)
13. A. Sabaa (e)
14. A. Sturm (j)

Affiliations:

a. GNS Science, Lower Hutt, New Zealand

b. Antarctic Research Centre, Victoria University of Wellington, Wellington, New Zealand

c. National Institute of Water and Atmospheric Research (NIWA), Wellington, New Zealand

d. School of Environment, University of Auckland, Auckland, New Zealand

e. Geomarine Research, Auckland, New Zealand

f. Research School of Earth Sciences, Australian National University, Canberra, Australia

g. Ciencias del Mar, Dept. of Geology, Universidad EAFIT, Medellin, Colombia

h. Department of Sustainability, Environment, Water, Population and Communities, Australian Antarctic Division, Kingston, Tasmania, Australia

i. Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Australia

j. Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany

Abstract:

Paleoceanographic archives derived from seventeen marine sediment cores reconstruct the response of the SW Pacific Ocean to the peak interglacial, Marine Isotope Stage (MIS) 5e (ca. 125 ka). Paleo-Sea Surface Temperature (SST) estimates were obtained from the Random Forest model – an ensemble decision tree tool - applied to core-top planktonic foraminiferal faunas calibrated to modern SSTs. The reconstructed geographic pattern of the SST anomaly (maximum SST between 120-132 ka minus mean modern SST) seems to indicate how MIS 5e conditions were generally warmer in the southwest Pacific, especially in the western Tasman Sea where a strengthened East Australian Current (EAC) likely extended subtropical influence to ca. 45oS off Tasmania. In contrast, the eastern Tasman Sea may have had a modest cooling except around 45oS. The observed pattern resembles that developing under the present warming trend in the region. An increase in wind stress curl over the modern South Pacific is hypothesized to have spun-up the South Pacific Subtropical Gyre, with concurrent increase in subtropical flow in the western boundary currents that include the EAC. However, warmer temperatures along the subtropical front and Campbell Plateau to the south suggest the relative influence of the boundary inflows to eastern New Zealand may have differed in MIS 5e, and these currents may have followed different paths compared to today.