New views of tropical paleoclimates from corals

Abstract

Corals o!er a rich archive of past climate variability in tropical ocean regions where instrumental data are limited and where our knowledge of multi-decadal climate sensitivity is incomplete. In the eastern equatorial Paci"c, coral isotopic records track variations in ENSO-related changes in sea-surface temperature; further west, corals record variability in sea-surface temperature and rainfall that accompanies zonal displacement of the Indonesian Low during ENSO events. These multi-century records reveal previously unrecognised ENSO variability on time scales of decades to centuries. Outside the ENSO-sensitive equatorial Paci"c, long-term trends towards recent warmer/wetter conditions suggest the tropics respond to global forcings. New coral paleothermometers indicate that surface-ocean temperatures in the tropical southwestern Paci"c were depressed by 4}63C during the Younger Dryas climatic event and rose episodically during the next 4000 yr. High temporal-resolution measurements of Sr/Ca and O in corals provide information about the surface-ocean hydrologic balance and can resolve the seasonal balance between precipitation and evaporation. Radiocarbon measurements in corals, coupled with ocean circulation models, may be used to reconstruct near-surface ocean circulation, past mixing rates, and the distribution of fossil fuel CO in the upper ocean. Most recently, seasonal to interannual variations in the radiocarbon of corals from the equatorial Paci"c have been linked to the redistribution of surface waters associated with the ENSO.

Evaluation of annual resolution coral geochemical records as climate proxies in the Great Barrier Reef of Australia

“…and elemental ratios (Sr/Ca, Mg/Ca, U/Ca, etc. ), obtained from massive reef-building corals can provide high-resolution records of past climatic conditions over timescales ranging from weekly to seasonal to annual as well as decades to centuries (Gagan et al 2000;Cole 2003;. To acquire seasonal to monthly climatic information, most studies sample coral skeletons at very high-resolution intervals (ca.…”

Increased seasonality in the Western Mediterranean during the last glacial from limpet shell geochemistry

“…Gagan et al, 2000 and references within)) has proved difficult, but recent work has shown that mollusc shells have significant potential as an archive of seasonalresolution SST at mid to high latitudes (e.g. Carré et al, 2005;Jones et al, 2005;Schöne et al, 2004).…”

“…Elderfield and Ganssen, 2000), and in aragonitic corals by using Sr/Ca ratios in conjunction with δ 18 O (e.g. Beck et al, 1997;Gagan et al, 2000). However there has been little success in identifying independent trace element palaeothermometers in the mollusc species so far examined (Carré et al, 2006;Freitas et al, 2005Freitas et al, , 2008Gentry et al, 2008;Takesue and Van Geen, 2004).…”

Wet and cold climate conditions recorded by coral geochemical proxies during the beginning of the first millennium CE in the northern South China Sea

“…Therefore, climate change records from the ocean will undoubtedly improve our knowledge of the evolution of climate change over various periods. Massive coral is one of the most reliable proxies for climatic and environmental change in the ocean, as it contains clear annual bands and has high growth rates, thereby recording high-resolution climate information from the surrounding seawater in which it lived (Gagan et al, 2000;Lough, 2010). The Sr/Ca ratios preserved in coral skeletons have long been used to reconstruct changes in sea surface temperature (SST; Smith et al, 1979;Beck et al, 1992), and δ 18 O values in coral reflect SST and δ 18 O in the ambient seawater (Swart and Coleman, 1980;Dunbar and Wellington, 1981).…”

“…The Sr/Ca ratios preserved in coral skeletons have long been used to reconstruct changes in sea surface temperature (SST; Smith et al, 1979;Beck et al, 1992), and δ 18 O values in coral reflect SST and δ 18 O in the ambient seawater (Swart and Coleman, 1980;Dunbar and Wellington, 1981). Residual δ 18 O (i.e., ∆δ 18 O), which is calculated by subtracting the contribution of temperature from coral δ 18 O, can be used as a tracer for seawater δ 18 O (δ 18 O sw ) and therefore salinity or rainfall (Mcculloch et al, 1994;Gagan et al, 1998;Gagan et al, 2000;Corrège, 2006;Deng et al, 2009;Deng et al, 2014b;Deng and Wei, 2015).…”