Last 35,000-year water column temperature and productivity variation in the Eastern Arabian Sea: monsoon and global climate connection

Abstract. A temporal increase of ~5‰ in the average nitrogen isotopic composition (δ15NPON) of surface particulate organic nitrogen was observed in the open north-eastern Arabian Sea during January to late February-early March 2003, despite the presence of T. erithraeum (up to ~11%), a diazotroph that fixes atmospheric N2, in the latter period. Hydrographic conditions and residence time of nitrate in the water column suggested that this increase could be a combined effect of denitrification in the subsurface layer and inefficient utilization of nitrate entrained in the water column during January.

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Monsoon variability during Mid Pliocene Warm Period: Evidence from oceanic denitrification at eastern Arabian Sea

10.5194/egusphere-egu21-12089 ◽

2021 ◽

Author(s):

Padmasini Behera ◽

Manish Tiwari

Keyword(s):

Organic Matter ◽

Surface Water ◽

Water Column ◽

Arabian Sea ◽

Water Productivity ◽

Warm Period ◽

Late Pliocene ◽

High Productivity ◽

Future Global Warming ◽

Eastern Arabian Sea

The variability of the South Asian Monsoon (SoAM) in warmer climatic conditions is not established yet. The Mid-Pliocene Warm Period (MPWP, 3.264 to 3.025 ma) is the most recent such event when the boundary conditions were similar to present with similar CO2 concentration (more than 400 ppmv) and temperature (2-3&#176;C higher than present). It presents the best analogue for understanding the impacts of future global warming on SoAM. The high-resolution study of denitrification from the eastern Arabian Sea can provide an insight into the SoAM variability during MPWP. Denitrification is the process by which nitrate is reduced to nitrogen gas (N2 or N2O) during organic matter decay in oxygen minima zones in the water column. The denitrification process enriches the nitrate pool with 15N, which is incorporated in the particulate organic matter. Denitrification is governed by the surface water productivity related to SoAM strength and the water column ventilation. We analyzed the nitrogen isotopic ratio of sedimentary organic matter (SOM, &#948;15NSOM) to examine the denitrification in the eastern Arabian Sea. Total nitrogen (TN %) and total organic carbon (TOC%) are used to estimate the surface water productivity from the sediment collected during expedition IODP 355, Hole U1456A. We find that the &#948;15NSOM values vary between 7-9 &#8240; during 3.22-3.15 Ma and 2.9-2.75 Ma indicating high denitrification. High &#948;15NSOM values coincide with high productivity as shown by both TN and TOC. It shows two major periods in the late Pliocene (3.22-3.15 Ma and 2.92-2.75 Ma) associated with stronger denitrification and high productivity. These results indicate the intensification of SoAM during warmer periods of Late Pliocene and at the start of intensification of Northern hemisphere glaciation. The enhanced denitrification during this period could possibly be due to a reduction in deep water ventilation and monsoon driven upsurge in productivity.

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Monsoon-induced changes in surface hydrography of the eastern Arabian Sea during the early Pleistocene

Geological Magazine ◽

10.1017/s0016756819000098 ◽

2019 ◽

Vol 157 (6) ◽

pp. 1001-1011 ◽

Cited By ~ 2

Author(s):

Rajeev Kumar Satpathy ◽

Stephan Steinke ◽

Arun Deo Singh

Keyword(s):

Water Column ◽

Asian Indian ◽

South Asian ◽

Mixed Layer ◽

Arabian Sea ◽

Early Pleistocene ◽

The South ◽

Eastern Arabian Sea ◽

Induced Changes ◽

South Asian Indian

AbstractUpper water column dynamics in the eastern Arabian Sea were reconstructed in order to investigate changes in the activity of the South Asian / Indian monsoon during the early Pleistocene (c. 1.5–2.7 Ma). We used planktic foraminiferal assemblage records combined with isotopic (δ18O and δ13C) data, Mg/Ca-based sea surface temperatures and seawater δ18O records to estimate changes in surface water conditions at International Ocean Discovery Program (IODP) Site U1457. Our records indicate two distinct regimes of monsoon-induced changes in upper water structure during the periods c. 1.55–1.65 Ma and c. 1.85–2.7 Ma. We infer that a more stratified upper water column and oligotrophic mixed layer conditions prevailed during the period 1.85–2.7 Ma, which may be due to overall weaker South Asian / Indian winter (NE) and summer (SW) monsoon circulations. The period 1.55–1.65 Ma was characterized by enhanced eutrophication of the mixed layer, which was probably triggered by intensified winter (NE) monsoonal winds. The long-term trend in hydrographic changes during 1.55–1.65 Ma appears to be superimposed by short-term variations, probably reflecting glacial/interglacial changes. We suggest that an intensification of the South Asian / Indian winter monsoon circulation occurred between ∼1.65 Ma and 1.85 Ma, which is most likely due to the development of strong meridional and zonal atmospheric circulations (i.e. Walker Circulation and Hadley Circulation) because of strong equatorial East–West Pacific temperature gradients.

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Monsoon related changes in sea surface productivity and water column denitrification in the Eastern Arabian Sea during the last glacial cycle

Marine Geology ◽

10.1016/j.margeo.2005.05.004 ◽

2005 ◽

Vol 219 (2-3) ◽

pp. 99-108 ◽

Cited By ~ 40

Author(s):

V.K. Banakar ◽

T. Oba ◽

A.R. Chodankar ◽

T. Kuramoto ◽

M. Yamamoto ◽

...

Keyword(s):

Water Column ◽

Arabian Sea ◽

Sea Surface ◽

Glacial Cycle ◽

Last Glacial ◽

Surface Productivity ◽

Eastern Arabian Sea ◽

The Last Glacial

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Hydrobiological responses of the North Eastern Arabian Sea during late winter and early spring inter-monsoons and the repercussions on open ocean blooms

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315416000795 ◽

2016 ◽

Vol 97 (7) ◽

pp. 1467-1478 ◽

Cited By ~ 6

Author(s):

K. B. Padmakumar ◽

Lathika Cicily Thomas ◽

K. G. Vimalkumar ◽

C. R. Asha Devi ◽

T. P. Maneesh ◽

...

Keyword(s):

Water Column ◽

Arabian Sea ◽

Early Spring ◽

Winter Monsoon ◽

Late Winter ◽

Biological Production ◽

Noctiluca Scintillans ◽

The North ◽

North Eastern ◽

Eastern Arabian Sea

Winter cooling and persistent mixing for more than a quarter of year (November to early March) along the North Eastern Arabian Sea (NEAS) results in nutrient enrichment of the euphotic column thereby triggering biological production. Hydrographic characteristics of NEAS during Late Winter Monsoon (LWM) and Early Spring Inter Monsoon (ESIM) and the influence on biological production are overviewed here. Winter convective mixing signatures were evident during LWM with low SST (24°C), high SSS (36.4), deep mixed layers (>100 m) and increased surface nitrate (~1 µM). Open ocean waters observed high chlorophyll a (1–2 mg m−3) and microphytoplankton abundance (1.2–1.5 × 104 cells l−1). Diatoms and green Noctiluca scintillans were the major microphytoplankton identified. ESIM observed gradual stabilization of water column with curtailment of winter signatures and strengthening of Noctiluca scintillans blooms. Mesozooplankton biomass was higher during LWM and decreased towards ESIM with intensification of Noctiluca blooms. However during ESIM, abundance of gelatinous zooplankton occurred in the bloom region. Inter-annual variations were observed in the biological responses along with the hydrographic changes. Thus the convective process during winter monsoon and stabilization of the water column during ESIM plays a significant role in the production pattern of NEAS.

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