N. Atlantic Salinity Change during the Last Century: Surface forcing at the salinity maximum propagated to the central Caribbean by subsurface waters
Abstract
Using multi-proxy records of salinity (δ 18O) and temperature (Sr/Ca, δ 18O) in the skeletons of sclerosponges, we have extended the instrumental records that suggest a recent adjustment in N. Atlantic salinity. Changes in salinity calculated using recent calibrations in sclerosponges between temperature and Sr/Ca and δ 18O, agree very well with the recent salinity increases of 0.3 documented by Curry et al. [2003] between the 1950's and 1990's. The sclerosponge data however indicate a continuous increase in salinity due to the increased heat availability of the earth's surface is less significant than salinity fluctuations related to the decadal scale forcing of the NAO. If these subsurface salinity records are related to surface forcing at the salinity maximum of the subtropical N. Atlantic where dry air masses from the Sahara cause very high net evaporation, one would expect the Bahamas records to be representative of a regional response as these waters form the shallow subsurface waters of much of the Caribbean. The Salinity Maximum surface Waters (SMW) of the N. Atlantic play a crucial role in the thermohaline circulation and the meridional transport of heat as they contribute to both the NADW and the subtropical-tropical meridional overturning cells (MOC's). Although the SMW source area of these subsurface waters is broad and diffuse, the salinity and temperature records from the Bahamas as well as previously published Sr/Ca and δ 18O records from Jamaica [Haase-Schramm et al., 2003] suggest a common N. Atlantic source but there are slight differences between the records such as stronger secular trends in the central Caribbean. However, comparison of subsurface sclerosponge salinity records in both locations indicate a regional salinity response to increased availability of heat to the oceans. Whether this response is a deepening of the mixed layer, a change in surface forcing of subsurface water masses, or a combination to the two remains enigmatic. References Curry, R., B. Dickson, and I. Yashahaev, A change in the freshwater balance of the Atlantic Ocean over the past four decades, Nature, 426, 826-829, 2003. Haase-Schramm, A., F. B\H{o}hm, A. Eisenhauer, and W. C. Dullo, Sr/Ca ratios and oxygen isotopes from sclerosponges: temperature history of the Caribbean mixed layer and thermocline during hte Little Ice Age, Paleoceanography, 18, doi: 10.1029/2002PA000830, 2003.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFMPP51C1346R
- Keywords:
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- 3670 Minor and trace element composition;
- 4267 Paleoceanography;
- 4283 Water masses;
- 1040 Isotopic composition/chemistry;
- 1635 Oceans (4203)