Reconstructing inter annual Indonesian river discharge by high-resolution LA-ICPMS geochemistry and UV-luminescence scanning of corals
Abstract
Degradation of many coral reefs around the world is linked to land-based activities. Soil erosion due to land-use changes results in increased quantities of sediment to local river systems which are, in many cases, discharged directly onto the reefs systems. The Berau delta/barrier reef system, located offshore NE Kalimantan, Indonesia, is characterized by a unique and pristine reef system that exists in close proximity of the Berau river mouth. Over the last decades deforestation and mining activities have considerably increased in the region. Our project aimed to assess the impact of those land-use changes in relation to sediment supply to the reef system over the last decades. Corals archive historical sedimentation records as they entrap terrigenous sediments into their skeleton and thus can be used to identify periods of decreased or enhanced sediment supply associated with anthropogenic induced land-use changes and natural variations in freshwater discharge. We investigate cores drilled from living Porites sp. coral colonies collected in the North Eastern part of the Berau delta >20 km from the river mouth. The annually banded cores were analyzed for Ba/Ca and Y/Ca ratios using LA-ICPMS in combination with spectral luminescence scanning (SLS) as a measure for terrestrial sediment input and soil erosion. Three coral luminescence records were used to establish a 28-year composite record of sediment discharge. The year to year variability of sediment supply to the reef system is evidently regulated by the El Niño Southern Oscillation climate system (ENSO). Especially positive phases of the Nino 3.4 index (= El Niño) have a strong negative effect on the sediment supply to the reef system which clearly diminished during the El Niño years 82-83, 92 and 97-98. We also conclude that for the Berau region, Y/Ca rather than Ba/Ca correlates well with precipitation records which is supported by the relation to the spectral luminescence results. Despite the fact that the population in the Berau region has increased 4-fold since the 1970's and extensive land clearing and coal mining has taken place since the early 1980's, we conclude that the amount of sediment supply to the reef system did not change significantly over the last three decades as no obvious trend in sediment supply could be identified in the coral cores.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMEP33B0914N
- Keywords:
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- 1616 GLOBAL CHANGE / Climate variability;
- 4808 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL / Chemical tracers;
- 4916 PALEOCEANOGRAPHY / Corals;
- 4922 PALEOCEANOGRAPHY / El Nino