Hanno Kinkel

Global Impact of the Panamanian Seaway Closure

Closure of the Isthmus of Panama about 3 million years ago (Ma) was accompanied by dramatic changes in Earths climate and biosphere. The Greenland ice sheet grew to continental extent and the great cycles of ice ages commenced dominating climate variability henceforth. Disruption of water mass exchange between the Atlantic and the Pacific Oceans led to different evolution of marine species on either side of the land bridge, while land-based organisms including mammals and other animals took the advantage to colonize an entire subcontinent. A 2-day workshop at the University of Kiel (Germany) summarized our current knowledge of this time period and identified areas for new research.

Response of the subtropical North Atlantic surface hydrography on deglacial and Holocene AMOC changes

The North Atlantic subtropical gyre (STG) circulates warm waters between 10 and 40 degrees N and is a potential area of heat storage during periods of reduced North Atlantic Meridional Overturning Circulation (AMOC), when warm salt-rich waters are retained in the subtropics. In this study, we investigated multicentennial to millennial scale changes in subtropical North Atlantic hydrography in response to AMOC changes during the last deglaciation and early Holocene, using sediment cores MD08-3180 and GEOFAR KF16. The coring site (38 degrees N) is situated near the boundary between transitional eastern North Atlantic waters and STG waters that is formed by the Azores Front. Hydrographic changes are reconstructed using new stable isotope data of benthic and subsurface dwelling planktonic foraminifera, Mg/Ca measurements on planktonic foraminifera, and planktonic foraminifera abundances that are supplemented with published sea surface temperature and stable isotope data. These multiproxy data indicate a close coupling between the latitudinal position of the northern STG boundary and deglacial AMOC modes. During weak AMOC phases (Heinrich event 1, Younger Dryas (YD), 8.2ka event), Northern Hemisphere subpolar water reached down to the northern STG boundary, displacing the boundary southward. During the BOlling-AllerOd warm period, a strong warming trend of the subtropical region to 19 degrees C is observed. A cooling of the sea surface temperature by 6 degrees C during the YD is accompanied by ongoing northward transport of warm subsurface water that might have contributed to the restart of AMOC.

Reticulofenestra calicis n. sp., an unusual small reticulofenestrid coccolith from the Lower Pliocene of the South Caribbean Sea

A new, very small to small (2.4 to 4.6mum) reticulofenestrid coccolith, Reticulofenestra calicis n. sp., is described by scanning electron and light microscopy from the Lower Pliocene (Zone CN11 of Okada and Bukry 1980) of the South Caribbean Sea. The coccolith shows typical reticulofenestrid distal and proximal shields but the distal shield is surmounted by a cup-shaped structure formed from extensions of the inner and outer tube elements. A new genus is not introduced, although this Structure is peculiar for reticulofenestrids. We base generic attribution on the distal shield morphology. The species occasionally has few slits between the distal shield elements. Attribution to the genera Reticulofenestra instead of Pseudoemiliania is discussed in detail. R. calicis n. sp. is structurally similar to the modern Emiliania huxleyi var. corona and to Reticulofenestra maceria. R. calicis n. sp., readily recognized under the light microscope in side view, has a short stratigraphic range. If the species proves not to be under strong ecological control, it will constitute a new biostratigraphic marker for subdivision of the R. pseudoumbilicus Zone.