TY  - JOUR
A1  - Steph, Silke
A1  - Tiedemann, Ralph
A1  - Prange, Matthias
A1  - Groeneveld, Jürgen
A1  - Schulz, Michael Karl
A1  - Timmermann, Axel
A1  - Nürnberg, Dirk
A1  - Rühlemann, Carsten
A1  - Saukel, Cornelia
A1  - Haug, Gerald H.
T1  - Early Pliocene increase in thermohaline overturning : a precondition for the development of the modern equatorial Pacific cold tongue
N2  - Unraveling the processes responsible for Earth's climate transition from an "El Nino-like state" during the warm early Pliocene into a modern-like "La Nina-dominated state" currently challenges the scientific community. Recently, the Pliocene climate switch has been linked to oceanic thermocline shoaling at similar to 3 million years ago along with Earth's final transition into a bipolar icehouse world. Here we present Pliocene proxy data and climate model results, which suggest an earlier timing of the Pliocene climate switch and a different chain of forcing mechanisms. We show that the increase in North Atlantic meridional overturning circulation between 4.8 and 4.0 million years ago, initiated by the progressive closure of the Central American Seaway, triggered overall shoaling of the tropical thermocline. This preconditioned the turnaround from a warm eastern equatorial Pacific to the modern equatorial cold tongue state about 1 million years earlier than previously assumed. Since similar to 3.6-3.5 million years ago, the intensification of Northern Hemisphere glaciation resulted in a strengthening of the trade winds, thereby amplifying upwelling and biogenic productivity at low latitudes.
Y1  - 2010
UR  - http://www.agu.org/journals/pa/
U6  - https://doi.org/10.1029/2008pa001645
SN  - 0883-8305
ER  - 
TY  - JOUR
A1  - Deplazes, Gaudenz
A1  - Lueckge, Andreas
A1  - Peterson, Larry C.
A1  - Timmermann, Axel
A1  - Hamann, Yvonne
A1  - Hughen, Konrad A.
A1  - Roehl, Ursula
A1  - Laj, Carlo
A1  - Cane, Mark A.
A1  - Sigman, Daniel M.
A1  - Haug, Gerald H.
T1  - Links between tropical rainfall and North Atlantic climate during the last glacial period
JF  - Nature geoscience
N2  - During the last glacial period, the North Atlantic region experienced pronounced, millennial-scale alternations between cold, stadial conditions and milder interstadial conditions-commonly referred to as Dansgaard-Oeschger oscillations-as well as periods of massive iceberg discharge known as Heinrich events(1). Changes in Northern Hemisphere temperature, as recorded in Greenland(2-4), are thought to have affected the location of the Atlantic intertropical convergence zone(5,6) and the strength of the Indian summer monsoon(7,8). Here we use high-resolution records of sediment colour-a measure of terrigenous versus biogenic content-from the Cariaco Basin off the coast of Venezuela and the Arabian Sea to assess teleconnections with the North Atlantic climate system during the last glacial period. The Cariaco record indicates that the intertropical convergence zone migrated seasonally over the site during mild stadial conditions, but was permanently displaced south of the basin during peak stadials and Heinrich events. In the Arabian Sea, we find evidence of a weak Indian summer monsoon during the stadial events. The tropical records show a more variable response to North Atlantic cooling than the Greenland temperature records. We therefore suggest that Greenland climate is especially sensitive to variations in the North Atlantic system-in particular sea-ice extent-whereas the intertropical convergence zone and Indian monsoon system respond primarily to variations in mean Northern Hemisphere temperature.
Y1  - 2013
U6  - https://doi.org/10.1038/ngeo1712
SN  - 1752-0894
VL  - 6
IS  - 3
SP  - 213
EP  - 217
PB  - Nature Publ. Group
CY  - New York
ER  - 
TY  - JOUR
A1  - Wolff, Christian Michael
A1  - Haug, Gerald H.
A1  - Timmermann, Axel
A1  - Damste, Jaap S. Sinninghe
A1  - Brauer, Achim
A1  - Sigman, Daniel M.
A1  - Cane, Mark A.
A1  - Verschuren, Dirk
T1  - Reduced interannual rainfall variability in East Africa during the last Ice Age
JF  - Science
N2  - Interannual rainfall variations in equatorial East Africa are tightly linked to the El Nino Southern Oscillation (ENSO), with more rain and flooding during El Nino and droughts in La Nina years, both having severe impacts on human habitation and food security. Here we report evidence from an annually laminated lake sediment record from southeastern Kenya for interannual to centennial-scale changes in ENSO-related rainfall variability during the last three millennia and for reductions in both the mean rate and the variability of rainfall in East Africa during the Last Glacial period. Climate model simulations support forward extrapolation from these lake sediment data that future warming will intensify the interannual variability of East Africa's rainfall.
Y1  - 2011
U6  - https://doi.org/10.1126/science.1203724
SN  - 0036-8075
VL  - 333
IS  - 6043
SP  - 743
EP  - 747
PB  - American Assoc. for the Advancement of Science
CY  - Washington
ER  -