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[MIS03-03] The influence of lithogenic matter supply on ballasting of particulate organic matter in the NE tropical Indian Ocean during the mid-Brunhes dissolution interval
Keywords:benthic foraminifera, ballasting, particulate organic matter, lithogenic matter
We investigated Quaternary benthic foraminifera and major element compositions in cores GPC04 and GPC03 (2991 m and 3650 m water depth, respectively; ~5ºN and ~90ºE) in the northeast tropical Indian Ocean (TIO) to consider the relationship of paleoceanographic phenomena between the surface and deep oceans during the mid-Brunhes dissolution interval, focusing on the ballasting effect of particulate organic matter (POM) since ~520 ka. The Bay of Bengal is characterized by the large amount of fresh water with lithogenic particles from the Ganga–Brahmputra–Meghna (GBM) River system. Rixen et al. (2019) observed seasonal variations in POM flux in the Bay of Bengal, suggesting the ballasting effects of POM by calcareous plankton skeletons and lithogenic matter.
In our study area, Nuttallides umbonifer tends to be more common at the shallower site (core GPC04) than at the deeper site (core GPC03). This species is usually reported from food-limited abyssal depths, living often between the lysocline and the calcium carbonate compensation depth (e.g., Mackensen et al., 1995). Thus, the common occurrence of N. umbonifer in core GPC04 during glacial periods is unusual, regarding its ecological conditions.
The Nuttallides rugosa (probably equivalent species of our N. umbonifer) was reported from the bathyal depth of the western Arabian Sea (Kurbjeweit et al., 2000) under common eolian supply of lithogenic matter (e.g., Ittekkot, 1991). In our study area, contributions of lithogenic matter and %N. umbonifer, showing the positive correlation in core GPC04, were unusually high under the better carbonate preservation conditions during glacial periods after ~370 ka. Hence, it is reasonable to suppose that the influence of lithogenic matter seemed more efficient during glacial periods. Intensified sea-level lowering during glacial periods after ~370 ka resulted in the more efficient delivery of riverine lithogenic matter and POM to the seafloor at the core sites, possibly through lateral transport along the continental slope (e.g., Ittekkot, 1991). Thus, riverine lithogenic matter from the GBM River system likely affects the deep-sea environment in the northeast TIO through the benthic-pelagic coupling of the surface and deep ocean (Thomas, 2007). Such sedimentation may be an important insight to consider paleoceanography in the Bay of Bengal with the Indian monsoon variations.
References:
1. Rixen et. al., 2019. The ballast effect of lithogenic matter and its influences on the carbon fluxes in the Indian Ocean. Biogeosci., 16, 485–503.
2. Mackensen et al., 1995. Deep-sea foraminifera in the South Atlantic Ocean: ecology and assemblage generation. Micropaleont., 41, 342–358.
3. Kurbjeweit et al., 2000. Distribution biomass and diversity of benthic foraminifera in relation to sediment geochemistry in the Arabian Sea. DSR II, 47, 2913–295.
4. Ittekkot, 1991. Particle flux studies in the Indian Ocean. EOS, 72, 527–530.
5. Thomas, 2007. Cenozoic mass extinctions in the deep sea: what perturbs the largest habitat on Earth? GSA, Special Paper, 424, 1–23.
In our study area, Nuttallides umbonifer tends to be more common at the shallower site (core GPC04) than at the deeper site (core GPC03). This species is usually reported from food-limited abyssal depths, living often between the lysocline and the calcium carbonate compensation depth (e.g., Mackensen et al., 1995). Thus, the common occurrence of N. umbonifer in core GPC04 during glacial periods is unusual, regarding its ecological conditions.
The Nuttallides rugosa (probably equivalent species of our N. umbonifer) was reported from the bathyal depth of the western Arabian Sea (Kurbjeweit et al., 2000) under common eolian supply of lithogenic matter (e.g., Ittekkot, 1991). In our study area, contributions of lithogenic matter and %N. umbonifer, showing the positive correlation in core GPC04, were unusually high under the better carbonate preservation conditions during glacial periods after ~370 ka. Hence, it is reasonable to suppose that the influence of lithogenic matter seemed more efficient during glacial periods. Intensified sea-level lowering during glacial periods after ~370 ka resulted in the more efficient delivery of riverine lithogenic matter and POM to the seafloor at the core sites, possibly through lateral transport along the continental slope (e.g., Ittekkot, 1991). Thus, riverine lithogenic matter from the GBM River system likely affects the deep-sea environment in the northeast TIO through the benthic-pelagic coupling of the surface and deep ocean (Thomas, 2007). Such sedimentation may be an important insight to consider paleoceanography in the Bay of Bengal with the Indian monsoon variations.
References:
1. Rixen et. al., 2019. The ballast effect of lithogenic matter and its influences on the carbon fluxes in the Indian Ocean. Biogeosci., 16, 485–503.
2. Mackensen et al., 1995. Deep-sea foraminifera in the South Atlantic Ocean: ecology and assemblage generation. Micropaleont., 41, 342–358.
3. Kurbjeweit et al., 2000. Distribution biomass and diversity of benthic foraminifera in relation to sediment geochemistry in the Arabian Sea. DSR II, 47, 2913–295.
4. Ittekkot, 1991. Particle flux studies in the Indian Ocean. EOS, 72, 527–530.
5. Thomas, 2007. Cenozoic mass extinctions in the deep sea: what perturbs the largest habitat on Earth? GSA, Special Paper, 424, 1–23.