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Caribbean sea surface conditions, 0-2ka and 6-8ka

Sea surface temperatures have been reconstructed for the time intervals 0-2000 and 6000-8000 years BP in the Caribbean from three cores.

Core JPA-02P, collected off the Virgin Islands, covers the period 800-1400BP.

Core PRP07 (273 cm long) from south of Puerto Rico (17º52.82 N; 66°35.90W; water depth 273 m) covers most of the last 2000 years. The chronology is based on eight AMS 14C dates on the planktonic foraminifer species Globigerinoides sacculifer. Accumulation rates range between 0.2 and 3.6 mm/yr.

The sediment core analyzed for the 6000-8000 BP interval, MD02-2582 (12.7 m long), was retrieved in 2002 by R/V Marion Dufresne from south of Puerto Rico (17º51.20N; 66º36.00W; water depth 380 m). Based on eight AMS 14C dates on G. sacculifer, the 6000-8000 BP interval was found between 37 and 44 cm. Accumulation rates range between 1.6 and 8.1 cm/kyr.

Planktonic foraminifer census data were generated from counts of more than 300 specimens from the >150 µm fraction at 1 cm intervals in both cores from Puerto Rico, 29 taxa were identified. Planktonic foraminifer relative abundances were converted to warm-season (WS; August-October) and cold-season (CS; February-March) paleo-SST estimates using artificial neural networks (ANN) trained on the GLAMAP data-set. The ANNs used for reconstructions of paleo-SSTs were selected based on their ability to optimally reproduce measured summer and winter SSTs 1951-1993 (COADS data) using a high-resolution box-core from south of Puerto Rico for which 15 samples of planktonic foraminifer census data were available from this time interval. Paleo-SST reconstructions are represented by averages obtained from 10 separate ANNs, with different training and test sets. The average root-mean-square-error of prediction (RMSEP) relative to the COADS SSTs is 0.31ºC for summer and 0.51ºC for winter. A comparison of WS paleo-SST estimates using different quantitative approaches indicates that the ANN technique generates estimates that are by far closer to the COADS 1951-1993 estimates than any of the other techniques, some of which yield unreasonably low or high estimates.

Present-day WS and CS SSTs in the NE Caribbean vary between 28.2 and 29.2°C, and 25.4 and 27.4°C, respectively (COADS 1951-1993 data). In the pre-1400 interval WS SSTs ranged between 28.2 and 28.6°C with a distinct low peak at about 1220 (27.8°C). CS SSTs ranged between 26.3 and 27.2°C, and a low value similar to that for the WS occurred at about 1220 (26.0°C). In the post-1400 part of the record distinctly low sea WS and CS SST anomalies occurred during the late 15th century and 1650 (minima of 28.2 and 26.2°C, respectively), associated with the Spörer and Maunder sunspot minima, respectively, and about 1920 (28.2 and 26.3°C, respectively). In addition, an extreme low CS peak is recorded in about 1975 (25.9°C). Highest WS SSTs are recorded in the 16th century (28.7-29.0 °C). Overall maximum CS SSTs are recorded in the late 15th and most of the 16th century (27.0-27.3°C).

A comparison with a climate reconstruction for western Europe (Guiot, 2005) through the last millennium indicates that the Little Ice Age (LIA) seems to have been considerably less pronounced in the Caribbean.

Estimated WS paleo-SSTs for the 6000-8000 BP time period (28.0-28.3°C) are cooler than most of the values for the 0-2000 BP period. This tendency is even stronger for the CS (paleo-SSTs in the range of 25.3-26.3°C). Hence, although the warmest climate of the Holocene would have been expected during the Holocene thermal maximum 6000-8000 years BP due to stronger solar insolation, relatively cool conditions appear to have prevailed in the Caribbean during this time interval.

Stable isotope analyses were carried out on core PRP07. The oxygen isotope record does not show any clear relationship to the paleo-SST, and are most likely influenced by local salinity variations, possibly induced by hurricanes.

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Department of Earth Sciences
Solvagen 17
761 64 NORRTALJE
Sweden
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