Abstract
Extreme climate events, such as the El Niños in 1997/1998 and 2015/16, have led to considerable forest loss in the Southeast Asian region following unprecedented drought and wildfires. In Borneo, the effects of extreme climate events have been exacerbated by rapid urbanization, accelerated deforestation and soil erosion since the 1980s. However, studies quantifying the impact of interannual and long-term (>3 decades) climatic and anthropogenic change affecting Borneo’s coastal and coral reef environments are lacking. Here, we used coral cores collected in Miri-Sibuti Coral Reefs National Park, Sarawak (Malaysia) to reconstruct the spatio-temporal dynamics of sea surface temperature and oxygen isotopic composition of seawater from 1982 to 2016, based on paired oxygen isotope and Sr/Ca measurements. The results revealed rising sea surface temperatures of 0.26 ± 0.04 °C per decade since 1982. Reconstructed δ18Osw displayed positive excursion during major El Niño events of 1983, 1997/98 and 2015/16, indicating drought conditions with less river runoff, rainfall and higher ocean salinities. La Niñas were generally associated with lower δ18Osw. We observed a long-term shift from more saline conditions between 1982 and 1995 towards less saline conditions after 1995, which are in agreement with the regional freshening trend, punctuated by saline excursion during El Niños. The decadal shifts were found to be driven by the Pacific Decadal Oscillation (PDO). This study provides the first long-term data on El Niño Southern Oscillation (ENSO)-driven synchrony of climate impacts on both terrestrial and marine ecosystems in northern Borneo. Our results suggest that coral records from northern Borneo are invaluable archives to detect regional ENSO and PDO impacts, and their interaction with the Asian-Australian monsoon, on the hydrological balance in the southern South China Sea beyond the past three decades.
Highlights
Southeast Asia (SEA) harbours an astonishing diversity of stony corals, comprising approximately 28% of the global total, located in the Maritime Continent[1,2]
The monthly interpolated time series of Anemone’s Garden (AG) and Eve’s Garden (EG) coral Sr/Ca and δ18O revealed a distinct seasonality with higher values during the winter season (December to February) and lower values in the summer season (June to August) (Fig. 3)
Our observed strong correlation between Sr/Ca and sea surface temperatures (SSTs) at the study sites indicates that growth rate and vital effects had an insignificant effect on skeletal Sr/Ca
Summary
Southeast Asia (SEA) harbours an astonishing diversity of stony corals, comprising approximately 28% of the global total, located in the Maritime Continent[1,2]. The aim of this work was to develop a spatio-temporal reconstruction of SST, oxygen isotopic composition of seawater tracking sea surface salinity (SSS) and river runoff dynamics based on a multi-proxy analysis of coral cores from two sites in MSCRNP, Borneo (Malaysia). Sr/Ca ratios in coral skeletons were utilized to reconstruct local SSTs. Combined Sr/ Ca and oxygen isotope analysis enabled us to reconstruct the oxygen isotopic composition of the seawater related to changes in the hydrological balance and salinity, covering the past three decades. Combined Sr/ Ca and oxygen isotope analysis enabled us to reconstruct the oxygen isotopic composition of the seawater related to changes in the hydrological balance and salinity, covering the past three decades This allowed for an unprecedented comparison to instrumental data from both land and sea from 1982 to 2016. Our results, were further investigated for signals of large-scale climatic teleconnections in northern Borneo, related to ENSO and the PDO
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