Sea surface temperature records in the northern South China Sea from mid‐Holocene coral Sr/Ca ratios

Abstract

[1] Three mid-Holocene sea surface temperature (SST) records spanning more than 30 years were reconstructed for the northern South China Sea using Sr/Ca ratios in Porites corals. The results indicate warmer than present climates between circa 6100 yr B.P. and circa 6500 yr B.P. with the mid-Holocene average minimum monthly winter SSTs, the average maximum monthly summer SSTs, and the average annual SSTs being about 0.5°-1.4°C, 0°-2.0°C, and 0.2°-1.5°C higher, respectively, than they were during 1970-1994. Summer SSTs decrease from circa 6500 yr B.P. to circa 6100 yr B.P. with a minimum centered at circa 6300 yr B.P. The higher average summer SSTs are consistent with a stronger summer monsoon during the midHolocene, and the decreasing trend indicates a secular decrease of summer monsoon strength, which reflects the change in summer insolation in the Northern Hemisphere. El Niño-Southern Oscillation (ENSO) cycles were apparent in both the mid-Holocene coral and modern instrumental records. However, the ENSO variability in the mid-Holocene SSTs was weaker than that in the modern record, and the SST record with the highest summer temperatures from circa 6460 yr B.P. to 6496 yr B.P. shows no robust ENSO cycle. This agrees with other studies that indicate that stronger summer monsoon circulation may have been associated with suppressed ENSO variability during the mid-Holocene.

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

“…The relationship between Sr/Ca and SST in 10AR2 obtained by a linear least squares regression is shown below. Sr=Ca  10 3 ¼ 11:209À0:0824  SST The intercept (A) and slope (B) values are very different to the previous Sr/Ca-SST relationships generated from highresolution coral series in which the values generally range from 9.760 to 10.956, and from -0.0393 to -0.0795 for A and B, respectively (Wei et al 2007). Despite these differences, a good linear regression line can be obtained when plotting A against B of the thermometer by annual calibration and other ones by monthly calibration compiled by Wei et al (Wei et al 2007; Fig.…”

“…Therefore, such annual resolution coral records offer a potential approach to reconstructing past climate change (Dunbar et al 1994;Cole et al 2000;Zinke et al 2014). This is especially the case for research into climate change (2002) and Wei et al (2007) over long timescales, in which annual resolution sampling can save much time and expense, but still provides similar information to studies based on high-resolution sampling. However, some important issues must be addressed when considering the use of annual resolution coral geochemical records in this field.…”

“…About 15 % of the samples were repeated, and the differences between the results of the repeated measurements were also within the range of analytical error. See Wei et al (2007) …”

“…To acquire seasonal to monthly climatic information, most studies sample coral skeletons at very high-resolution intervals (ca. 1 mm or less; e.g., McCulloch et al 1994;Alibert and McCulloch 1997;Gagan et al 1998;McCulloch et al 1999;Sun et al 2004;Wei et al 2007;Deng et al 2009;Duprey et al 2012;DeLong et al 2013). However, high-resolution sampling requires a considerable number of subsamples for analysis, which makes coral-based climate reconstructions time consuming, labor intensive, and expensive.…”

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 records from the SCS are important for the study of climate change over periods of significant change such as the MWP and LIA. In recent years, there have been a number of successful studies of past climate change based on coral records from the mid-Holocene to the CWP in the SCS (e.g., Sun et al, 2005;Yu et al, 2005;Wei et al, 2007;Liu et al, 2008;Deng et al, 2009;Chiang et al, 2010;Yu, 2012;Chen et al, 2013;Deng et al, 2013;Liu et al, 2013;Deng et al, 2014b;Deng and Wei, 2015;Yang et al, 2015). However, climate records that cover the past two millennia remain limited.…”