Central Tropical Pacific SST and Salinity Variability over the Little Ice Age

Abstract:

Anthropogenic trends are difficult to separate from natural variability in the tropical Pacific, where instrumental data coverage is sparse. Of particular interest are variations of climate in the pre-industrial era, but instrumental data from this time period is virtually nonexistent. Corals allow for the investigation of pre-industrial climate variability, but most living coral colonies rarely span more than a century. Fossil corals provide a valuable archive of climate variability over the past millennia [Cobb et al., 2013] and are best suited to the reconstruction of ENSO. For the reconstruction of mean climate, systematic offsets between proxy records from contemporaneous corals translates to large error bars on the resulting reconstructions [e.g. Felis et al., 2003; Pfeiffer et al., 2009]. By building composite paleoclimate records using multiple corals from the Line Islands (2°N – 6°N, 157°W – 162°W), we quantify mean climate state and climate variability in the central tropical Pacific (CTP) during the Little Ice Age (LIA). We compare paired d¹⁸O and Sr/Ca records from Line Island fossil corals to a large collection of modern coral d¹⁸O and Sr/Ca records from the same islands to estimate SST and salinity changes from the LIA to the late 20^th century. Taken together, Sr/Ca records from three Palmyra Atoll fossil corals spanning 1630-1703CE suggest CTP temperatures may have been 1.7±0.9˚C cooler during much of the 17^th century. Reconstructed seawater d¹⁸O values are indicative of drier conditions at Palmyra, consistent with a southward shift of the ITCZ during the LIA documented in sediments from the Line Islands [Sachs et al., 2009]. We compare the results from seven LIA-dated fossil corals from nearby Christmas Island (Kiritimati; 2˚N, 157˚W) to the results obtained from Palmyra, enabling us to resolve potential shifts in the meridional gradients of SST and hydrology in this region during the LIA.

References:
Cobb, K. M., et al. (2013) Science. doi: 10.1126/science.1228246
Felis, T., et al. (2003) Coral Reefs. doi: 10.1007/s00338-003-0324-3
Pfeiffer, M., et al. (2009) Int. J. Earth Sci. doi: 10.1007/S00531-008-0326-Z
Sachs, J. P., et al. (2009) Nature Geoscience. doi: 10.1038/ngeo554