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

Mapping Intimacies ◽

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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Assessing controls on organic matter enrichments in hemipelagic homogenous marls of the Cretaceous Vocontian Basin (France): an unexpected variability observed from multiple organic-rich levels

BSGF - Earth Sciences Bulletin ◽

10.1051/bsgf/2022001 ◽

2022 ◽

Author(s):

Alexis Caillaud ◽

Melesio Quijada ◽

Stephan R. Hlohowskyj ◽

Anthony Chappaz ◽

Viviane Bout-Roumazeilles ◽

...

Keyword(s):

Organic Matter ◽

Surface Water ◽

Sea Level ◽

Water Productivity ◽

The Other ◽

Redox Conditions ◽

Accumulation Rates ◽

High Productivity ◽

Anoxic Events ◽

Parameter Approach

The Marnes Bleues Formation from the Vocontian Basin (Southeastern France) shows many organic rich levels, some concomitant to oceanic anoxic events OAE1a and OAE1b. These organic-rich levels are scattered through a thick homogeneous succession of marls, poor in organic matter (OM). Through a multi-parameter approach, the organic-rich levels from the Aptian-Albian were characterized. Our results show that all OM-rich levels exhibit variable characteristics, such as OM nature (marine vs. continental), sedimentation and accumulation rates, redox conditions, surface-water productivity and relative sea level, but they all show low to modest enrichments in OM. Furthermore, all the levels share in common the fact that they formed under conditions of normal to low productivity and oxic to suboxic conditions. Thus, our results strongly suggest that, in the absence of high productivity and anoxic bottom conditions, the other factors reputed to favor OM accumulation only led to sporadic and low enrichments in organic contents. It is as if such factors could only enhance OM accumulation but could not induce it alone. What was true for the Vocontian Basin may be extended to other settings, regardless of their time of deposition or location.

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Effects of Fe addition on sediment P dynamics in a eutrophic lake

10.5194/egusphere-egu21-4941 ◽

2021 ◽

Author(s):

Melanie Münch ◽

Rianne van Kaam ◽

Karel As ◽

Stefan Peiffer ◽

Gerard ter Heerdt ◽

...

Keyword(s):

Water Quality ◽

Organic Matter ◽

Surface Water ◽

Water Column ◽

Sediment Cores ◽

Surface Water Quality ◽

Water Interface ◽

Eutrophic Lakes ◽

Fe Addition

The decline of surface water quality due to excess phosphorus (P) input is a global problem of increasing urgency. Finding sustainable measures to restore the surface water quality of eutrophic lakes with respect to P, other than by decreasing P inputs, remains a challenge. The addition of iron (Fe) salts has been shown to be effective in removing dissolved phosphate from the water column of eutrophic lakes. However, the resulting changes in biogeochemical processes in sediments as well as the long-term effects of Fe additions on P dynamics in both sediments and the water column are not well understood.In this study, we assess the impact of past Fe additions on the sediment P biogeochemistry of Lake Terra Nova, a well-mixed shallow peat lake in the Netherlands. The Fe-treatment in 2010 efficiently reduced P release from the sediments to the surface waters for 6 years. Since then, the internal sediment P source in the lake has been increasing again with a growing trend over the years.In 2020, we sampled sediments at three locations in Terra Nova, of which one received two times more Fe during treatment than the other two. Sediment cores from all sites were sectioned under oxygen-free conditions. Both the porewaters and sediments were analysed for their chemical composition, with sequential extractions providing insight into the sediment forms of P and Fe. Additional sediment cores were incubated under oxic and anoxic conditions and the respective fluxes of P and Fe across the sediment water interface were measured.The results suggest that Fe and P dynamics in the lake sediments are strongly coupled. We also find that the P dynamics are sensitive to the amount of Fe supplied, even though enhanced burial of P in the sediment was not detected. The results of the sequential extraction procedure for P, which distinguishes P associated with humic acids and Fe oxides, as well as reduced flux of Fe(II) across the sediment water interface in the anoxic incubations, suggest a major role of organic matter in the interaction of Fe and P in these sediments.Further research will include investigations of the role of organic matter and sulphur in determining the success of Fe-treatment in sequestering P in lake sediments. Based on these data in combination with reactive transport modelling we aim to constrain conditions for successful lake restoration through Fe addition.

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Amino acid composition and δ15N of suspended matter in the Arabian Sea: implications for organic matter sources and degradation

Biogeosciences ◽

10.5194/bg-10-7689-2013 ◽

2013 ◽

Vol 10 (11) ◽

pp. 7689-7702 ◽

Cited By ~ 7

Author(s):

B. Gaye ◽

B. Nagel ◽

K. Dähnke ◽

T. Rixen ◽

N. Lahajnar ◽

...

Keyword(s):

Organic Matter ◽

Amino Acid ◽

Water Column ◽

Residence Time ◽

Mixed Layer ◽

Suspended Matter ◽

Arabian Sea ◽

Monsoon Season ◽

Sediment Traps ◽

Surface Mixed Layer

Abstract. Sedimentation in the ocean is fed by large aggregates produced in the surface mixed layer that sink rapidly through the water column. These particles sampled by sediment traps have often been proposed to interact by disaggregation and scavenging with a pool of fine suspended matter with very slow sinking velocities and thus a long residence time. We investigated the amino acid (AA) composition and stable nitrogen isotopic ratios of suspended matter (SPM) sampled during the late SW monsoon season in the Arabian Sea and compared them to those of sinking particles to understand organic matter degradation/modification during passage through the water column. We found that AA composition of mixed layer suspended matter corresponds more to fresh plankton and their aggregates, whereas AA composition of SPM in the sub-thermocline water column deviated progressively from mixed layer composition. We conclude that suspended matter in deep waters and in the mixed layers of oligotrophic stations is dominated by fine material that has a long residence time and organic matter that is resistant to degradation. SPM in areas of high primary productivity is essentially derived from fresh plankton and thus has a strong imprint of the subsurface nitrate source, whereas SPM at oligotrophic stations and at subthermocline depths appears to exchange amino acids and nitrogen isotopes with the dissolved organic carbon (DOC) pool influencing also the δ15N values.

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

Geo-Marine Letters ◽

10.1007/s00367-019-00570-6 ◽

2019 ◽

Vol 39 (3) ◽

pp. 239-248

Author(s):

A Rajasree ◽

Vikesano R. Punyu ◽

Virupaxa K. Banakar

Keyword(s):

Water Column ◽

Arabian Sea ◽

Global Climate ◽

Column Temperature ◽

Eastern Arabian Sea

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15N enrichment in the surface Particulate Organic Nitrogen of the north-eastern Arabian Sea from the middle to the waning phase of the winter monsoon: possible causes

Ocean Science Discussions ◽

10.5194/osd-4-245-2007 ◽

2007 ◽

Vol 4 (1) ◽

pp. 245-264

Author(s):

S. Kumar ◽

R. Ramesh

Keyword(s):

Water Column ◽

Arabian Sea ◽

Organic Nitrogen ◽

Subsurface Layer ◽

The North ◽

North Eastern ◽

Eastern Arabian Sea ◽

Nitrogen Isotopic Composition ◽

Hydrographic Conditions ◽

N Enrichment

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-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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Amino acid composition and δ15N of suspended matter in the Arabian Sea

Biogeosciences Discussions ◽

10.5194/bgd-10-13317-2013 ◽

2013 ◽

Vol 10 (8) ◽

pp. 13317-13352

Author(s):

B. Gaye ◽

B. Nagel ◽

K. Dähnke ◽

T. Rixen ◽

N. Lahajnar ◽

...

Keyword(s):

Organic Matter ◽

Amino Acid ◽

Amino Acid Composition ◽

Water Column ◽

Acid Composition ◽

Residence Time ◽

Mixed Layer ◽

Suspended Matter ◽

Arabian Sea ◽

Surface Mixed Layer

Abstract. Sedimentation in the ocean is fed by large aggregates produced in the surface mixed layer that sink rapidly through the water column. These particles sampled by sediment traps have often been proposed to interact by disaggregation and scavenging with a pool of fine suspended matter with very slow sinking velocities and thus a long residence time. We investigated the amino acid composition and stable nitrogen isotopic ratios of suspended matter sampled during the late SW monsoon season in the Arabian Sea and compared them to those of sinking particles to investigate organic matter degradation/modification during passage through the water column. We found that amino acid (AA) composition of mixed layer suspended matter corresponds more to fresh plankton and their aggregates, whereas AA composition of suspended matter in the sub-thermocline water column deviated progressively from mixed layer composition. We conclude that suspended matter in deep waters and in the mixed layers of oligotrophic stations is dominated by fine material that has a long residence time and organic matter that is resistant to degradation. Whereas SPM in areas of high primary productivity is essentially derived from fresh plankton and thus has a strong imprint of the subsurface nitrate source, SPM at oligotrophic stations and at subthermocline depths appears to exchange amino acids with the DOC pool influencing also the δ15N values.

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Climate variability and ocean fertility during the Aptian Stage

Climate of the Past ◽

10.5194/cp-11-383-2015 ◽

2015 ◽

Vol 11 (3) ◽

pp. 383-402 ◽

Cited By ~ 52

Author(s):

C. Bottini ◽

E. Erba ◽

D. Tiraboschi ◽

H. C. Jenkyns ◽

S. Schouten ◽

...

Keyword(s):

Organic Matter ◽

Surface Water ◽

Climatic Conditions ◽

Low Fertility ◽

Ontong Java Plateau ◽

Direct Role ◽

High Productivity ◽

Oceanic Anoxic Event ◽

Continental Runoff ◽

Maximum Warming

Abstract. Several studies have been conducted to reconstruct temperature variations across the Aptian Stage, particularly during early Aptian Oceanic Anoxic Event (OAE) 1a. There is a general consensus that a major warming characterized OAE 1a, although some studies have provided evidence for transient "cold snaps" or cooler intervals during the event. The climatic conditions for the middle–late Aptian are less constrained, and a complete record through the Aptian is not available. Here we present a reconstruction of surface-water palaeotemperature and fertility based on calcareous nannofossil records from the Cismon and Piobbico cores (Tethys) and DSDP Site 463 (Pacific Ocean). The data, integrated with oxygen-isotope and TEX86 records, provide a detailed picture of climatic and ocean fertility changes during the Aptian Stage, which are discussed in relation to the direct/indirect role of volcanism. Warm temperatures characterized the pre-OAE 1a interval, followed by a maximum warming (of ~ 1.5–2 °C) during the early phase of anoxia under intense volcanic activity of the Ontong Java Plateau (OJP). A short-lived cooling episode interrupted the major warming, following a rapid increase in weathering rates. Nannofossils indicate that mesotrophic conditions were reached when temperatures were at their highest and OJP volcanism most intense, thus suggesting that continental runoff, together with increased input of hydrothermal metals, increased nutrient supply to the oceans. The latter part of OAE 1a was characterized by cooling events, probably promoted by CO2 sequestration during burial of organic matter. In this phase, high productivity was probably maintained by N2-fixing cyanobacteria, while nannofossil taxa indicating higher fertility were rare. The end of anoxia coincided with the cessation of volcanism and a pronounced cooling. The mid-Aptian was characterized by highest surface-water fertility and progressively decreasing temperatures, probably resulting from intense continental weathering drawing down pCO2. The lowest temperatures, combined with low fertility, were reached in the middle–late Aptian across the interval characterized by blooming of Nannoconus truittii. The prolonged cooling was followed by significant warming across the Aptian–Albian boundary. The data presented suggest that OJP activity played a direct role in inducing global warming during the early Aptian, whereas other mechanisms (weathering, deposition of organic matter) acted as feedback processes, favouring temporary cooler interludes.

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