[1] Strontium to calcium ratios (Sr/Ca) are reported for a massive brain coral Diploria labyrinthiformis collected from the south shore of Bermuda and are strongly correlated with both sea surface temperature (SST) and mean annual skeletal growth rate. High Sr/Ca ratios correspond with cold SSTs and slow skeletal growth rate and vice versa. We provide a quantitative calibration of Sr/Ca to extension rate and SST along the axis of maximum growth and derive a growth-dependent Sr/Ca-SST calibration equation to reconstruct western subtropical North Atlantic SSTs for the past 223 years. When the influence of growth rate is excluded from the calibration, Sr/Ca ratios yield SSTs that are too cold during cool anomalies and too warm during warm anomalies. Toward the end of the Little Ice Age ($1850), SST changes derived using a calibration that is not growth-dependent are exaggerated by a factor of 2 relative to those from the growth-corrected model that yields SSTs $1.5°C cooler than today. Our results indicate that incorporation of growth rate effects into coral Sr/Ca calibrations may improve the accuracy of SSTs derived from living and fossil corals.

No abstract

[1] Combining strontium-to-calcium ratios (Sr/Ca) with mean annual growth rates in Bermuda Diploria labyrinthiformis (brain corals) is shown to improve sea surface temperature (SST) calibrations relative to instrumental data. Growth-corrected Sr/Ca-SST calibrations based on single-coral colonies over the same calibration interval, however, are found to be poorly suited for application to data from different coral colonies. This raises concerns about the accuracy of SST reconstructions from fossil coral measurements that involve extrapolation beyond the range of values seen during the calibration period. Here we pursue a novel approach to this problem by incorporating data from multiple coral colonies into a single growth-corrected Sr/Ca-SST calibration equation, effectively expanding the range of modern values constraining the model. The use of a multiple-colony calibration model for reconstructing SST yields greater precision and accuracy relative to instrumental data than single-colony models, providing greater confidence for applications to fossil coral samples.Citation: Goodkin, N. F., K. A. Hughen, and A. L. Cohen (2007), A multicoral calibration method to approximate a universal equation relating Sr/Ca and growth rate to sea surface temperature, Paleoceanography, 22, PA1214,

Hong Kong's coastal waters afford a marginal environment for coral reef growth, with high seasonal and short-term variability in water temperatures (ranging from <14°C in winter to 31°C in summer), and low summer salinity (as low as 15 psu) due to runoff associated with the Asian wet monsoon season and the Pearl River Delta. Yet Hong Kong hosts 84 reef-building coral species in 28 genera of 12 families of the Scleractinia, distributed in 5 broad communities with strong geographic and environmental affinities and key indicator species. Coral communities farthest from the influence of the Pearl River Delta have relatively high sea bed coverage and species diversity (30 to 50% coverage, and > 30 spp. per site), and also host some large, old corals. X-radiographs of a core of one massive Porites colony confirms ~200 yr of growth, with 2 short-term periods of mortality, hidden in the skeleton by overgrowth. Very low linear extension rates (< 4 mm yr -1 ) in this coral and 2 others are anomalous for Porites corals and are indicative of the high-stress environment. Low growth rates suggest that other Hong Kong corals, despite the harsh environmental conditions, may also live for centuries, contributing to the development of 'incipient reefs'. KEY WORDS: Hong Kong · Long-lived massive corals · Porites · South China SeaResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 426: 185-196, 2011 ate framework, slow or stunted growth rates, and decreased depth distribution (Harriott & Banks 2002). The lack of framework in these communities is primarily attributable to a lack of significant calcium carbonate accretion (Buddemeier & Smith 1999, Kleypas et al. 1999b. In many instances corals in these communities attach to hard substrata as isolated colonies growing on exposed bedrock (e.g. Macintyre 2003). Although coral communities can have species diversity similar to that of true coral reefs (>140 spp. in the Indo-Pacific region; Sheppard & Sheppard 1991, Perry 2003, most have much lower species diversity (< 90 spp.; Harriott & Banks 2002, Moyer et al. 2003, Nozawa et al. 2008.One such marginal environment hosting coral communities is the area around Hong Kong. Hong Kong (22' 20°N, 114' 11°E) lies on the southern Chinese coast, in the tropics, some 320 km south of the Tropic of Cancer (Fig. 1). Hong Kong waters experience a range of temperatures (from 14 to 31°C) and salinities (typically 24 to 25 practical salinity units, or psu, comparable to ppt) generated by the interplay of the monsoonal systems, changing ocean currents, and freshwater discharge (Tang & Ni 1996, Lee & Liu 1998. Hence the coral communities of Hong Kong are living at the edge of their physiological tolerances (e.g. Veron 1995, Harriott 1999. Episodic widespread partial-to-total colony mortality and localized community mortality of corals and other tropical marine species are observed at meteorological or oceanographic extremes (e.g. precipitation events or sea surface temperature [SST] minima;McCorry...

The double Intertropical Convergence Zone bias remains a persistent problem in coupled general circulation model simulations. Due to the strong sea surface temperature (SST)‐convection relationship in the tropics, precipitation biases are sensitive to background SST. Using historical simulations of 24 coupled general circulation models and an atmospheric general circulation model, we show that cold equatorial SST biases at least exacerbate double Intertropical Convergence Zone biases in the Pacific. A linear regression model is used to demonstrate that improved predictability of precipitation trends is possible with such model‐dependent information as mean‐state SST biases accompanying projected SST trends. These results provide a better understanding of the root of the double Intertropical Convergence Zone bias and a possible path to reduced uncertainty in future tropical precipitation trends.

No abstract

The Indonesian Throughflow (ITF) is a globally important ocean current that fuels heat and buoyancy fluxes throughout the Indo‐Pacific and is known to covary in strength with the El Niño Southern Oscillation at interannual time scales. A climate system with a less well‐quantified impact on the ITF is the East Asian Winter Monsoon (EAWM), which drives less saline surface waters from the South China Sea (SCS) into the Makassar Strait, obstructing surface ITF flow. We present a subannually resolved record of sea surface salinity (SSS) from 1927 to 2011 based on coral δ18O from the Makassar Strait that reveals variability in the relative contributions of different source waters to the surface waters of the Makassar Strait during the boreal winter monsoon. We find that the EAWM (January–March) strongly influences interannual SSS variability during boreal winter over the twentieth century (r = 0.54, p << 0.0001), impacting surface water circulation in the SCS and Indonesian Seas.

Reconstructions of key climate parameters prior to anthropogenic influences serve to constrain decadal to multicentury natural climate variability. In the western Pacific region, relatively few reconstructions exist north of the Western Pacific Warm Pool (WPWP), a region critical to global climate. In this study, we collected a coral core from Houbihu, southern Taiwan, and generated a 225-year reconstruction of annual and wintertime sea surface temperature, dry season sea surface salinity, and wet season rainfall records derived from paired Porites Sr/Ca and δ 18 O profiles extending back to the end of the Little Ice Age (1850 CE). Multidecadal sea surface temperature trends generally track regional surface temperature reconstructions, indicating the dominant influence of solar and volcanic radiative forcings. Reconstructed dry season sea surface salinity reflects an advection signal linked to the East Asian Winter Monsoon and the Pacific Decadal Oscillation, both influencing variations in the Kuroshio Intrusion across the Luzon Strait. Reconstructed wet season rainfall, on the other hand, reveals influence of the Pacific Decadal Oscillation on the decadal variability of local and regional rainfall patterns. Relative to the late 1900s, our climate reconstructions document cooler and drier (high salinity and low rainfall) conditions during the end of the Little Ice Age, supporting other lines of evidence of a retracted WPWP region during this period. In the late 20th to early 21st century, our climate reconstructions record warming and freshening (low salinity and high rainfall) trends, highlighting the potential impact of anthropogenic forcing in the extension of the WPWP.