TY  - JOUR
A1  - Regenberg, Marcus
A1  - Steph, Silke
A1  - Nuernberg, Dirk
A1  - Tiedemann, Ralph
A1  - Garbe-Schoenberg, Dieter
T1  - Calibrating Mg/Ca ratios of multiple planktonic foraminiferal species with delta O-18-calcification temperatures : paleothermometry for the upper water column
N2  - In order to consistently approximate the thermal vertical structure of past upper water columns, Mg/Ca ratios of eight planktonic foraminiferal species with different preferential calcification depths selected from 76 tropical Atlantic and Caribbean sediment-surface samples were calibrated with delta O-18-derived calcification temperatures with an overall range of approximate to 8-28 degrees C. Extending the broad number of species-specific calibrations, which agree well especially with our shallow-dweller calibrations, this study presents new bulk calcite Mg/Ca vs. calcification temperature relationships for shallow-dwelling Globigerinoides ruber pink, thermocline-dwelling Globorotalia menardii, and deep-dwelling Globorotalia truncatulinoides dextral and Globorotalia crassaformis not separately calibrated before. The species-specific temperature sensitivities are relatively similar (approximate to 7- 11% increase in Mg/Ca per 1 degrees C), yet y-axis intercepts vary from 0.23-0.65 for the shallow and thermocline dwellers to 0.83-1.32 for the deep dwellers. Based on these differences, we established a 'warm water' calibration for temperatures > 19 degrees C (Mg/Ca=0.29.exp(0.101.T): r=0.90; shallow and thermocline dwellers) and a 'cold water' calibration for temperatures < 15 degrees C (Mg/Ca=0.84.exp(0.083.T); r=0.85; deep dwellers). These calibrations are offset by approximate to 8 degrees C. This maybe significant for paleotemperature reconstructions, which are afflicted with the problem that similar Mg/Ca offsets are probably characteristic of extinct species used to calculate past temperatures.
Y1  - 2009
UR  - http://www.sciencedirect.com/science/journal/0012821X
U6  - https://doi.org/10.1016/j.epsl.2008.12.019
SN  - 0012-821X
ER  - 
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  -