Millennial/centennial-scale thermocline ventilation changes in the Indian Ocean as reflected by aragonite preservation and geochemical variations in Arabian Sea sediments

Böning, Philipp; Bard, Édouard

doi:10.1016/j.gca.2009.08.028

Cited by 64 publications

(97 citation statements)

References 87 publications

(169 reference statements)

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“…Aragonite preservations and δ 13 C of benthic foraminifera further suggest that enhanced formation of GAAIW ventilated the lower OMZ from about 800 to 1800 m, especially during stadials (Böning and Bard, 2009;Jung et al, 2009;Naidu et al, 2014;Schmiedl and Leuschner, 2005). A similar increase in GAAIW formation was observed in the Atlantic and Pacific and was explained by the strong reduction of NADW formation and a simultaneous strengthening of SAMW and GAAIW formation due to the reduced salinity and density of North Atlantic surface water (Rickaby and Elderfield, 2005;Ronge et al, 2015).…”

Section: Nitrogen Cycling In the Glacialmentioning

confidence: 82%

“…At present, SAMW is the major oxygen source to the Arabian Sea OMZ, while PGW, RSW, and IIW are only small contributors of oxygen (Fine et al, 2008;You, 1998). During glacial conditions, the increased SAMW production occurred further north due to the northward shift of the subpolar front similar to the GAAIW (Rickaby and Elderfield, 2005) and better ventilated the upper OMZ (Böning and Bard, 2009). It carried more oxygen due to less mixing with IIW and RSW, and an accelerated circulation (Böning and Bard, 2009) led to a lower residence time in the Arabian Sea.…”

Section: Nitrogen Cycling In the Glacialmentioning

confidence: 96%

“…During glacial conditions, the increased SAMW production occurred further north due to the northward shift of the subpolar front similar to the GAAIW (Rickaby and Elderfield, 2005) and better ventilated the upper OMZ (Böning and Bard, 2009). It carried more oxygen due to less mixing with IIW and RSW, and an accelerated circulation (Böning and Bard, 2009) led to a lower residence time in the Arabian Sea. Moreover, it is quite possible that glacial SAMW carried fewer preformed nutrients due to the better nutrient utilization related to increased eolian supply of phosphate and trace metals to the region of SAMW formation (Somes et al, 2017).…”

Section: Nitrogen Cycling In the Glacialmentioning

confidence: 97%

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Glacial–interglacial changes and Holocene variations in Arabian Sea denitrification

et al. 2018

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Abstract. At present, the Arabian Sea has a permanent oxygen minimum zone (OMZ) at water depths between about 100 and 1200 m. Active denitrification in the upper part of the OMZ is recorded by enhanced δ 15 N values in the sediments. Sediment cores show a δ 15 N increase during the middle and late Holocene, which is contrary to the trend in the other two regions of water column denitrification in the eastern tropical North and South Pacific. We calculated composite sea surface temperature (SST) and δ 15 N ratios in time slices of 1000 years of the last 25 kyr to better understand the reasons for the establishment of the Arabian Sea OMZ and its response to changes in the Asian monsoon system. Low δ 15 N values of 4-7 ‰ during the last glacial maximum (LGM) and stadials (Younger Dryas and Heinrich events) suggest that denitrification was inactive or weak during Pleistocene cold phases, while warm interstadials (ISs) had elevated δ 15 N. Fast changes in upwelling intensities and OMZ ventilation from the Antarctic were responsible for these strong millennial-scale variations during the glacial. During the entire Holocene δ 15 N values > 6 ‰ indicate a relatively stable OMZ with enhanced denitrification. The OMZ develops parallel to the strengthening of the SW monsoon and monsoonal upwelling after the LGM. Despite the relatively stable climatic conditions of the Holocene, the δ 15 N records show regionally different trends in the Arabian Sea. In the upwelling areas in the western part of the basin, δ 15 N values are lower during the mid-Holocene (4.2-8.2 ka BP) compared to the late Holocene (< 4.2 ka BP) due to stronger ventilation of the OMZ during the period of the most intense southwest monsoonal upwelling. In contrast, δ 15 N values in the northern and eastern Arabian Sea rose during the last 8 kyr. The displacement of the core of the OMZ from the region of maximum productivity in the western Arabian Sea to its present position in the northeast was established during the middle and late Holocene. This was probably caused by (i) reduced ventilation due to a longer residence time of OMZ waters and (ii) augmented by rising oxygen consumption due to enhanced northeast-monsoon-driven biological productivity. This concurs with the results of the Kiel Climate Model, which show an increase in OMZ volume during the last 9 kyr related to the increasing age of the OMZ water mass.

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Section: Nitrogen Cycling In the Glacialmentioning

confidence: 82%

Section: Nitrogen Cycling In the Glacialmentioning

confidence: 96%

Section: Nitrogen Cycling In the Glacialmentioning

confidence: 97%

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Glacial–interglacial changes and Holocene variations in Arabian Sea denitrification

et al. 2018

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“…Our study also confirms the potential for the Arabian Sea OMZ to strongly impact the marine nitrogen budget at a larger scale in response to Indian monsoon fluctuations, in agreement with conclusions of previous paleo- studies. Besides monsoon strength, some studies have linked past OMZ intensity changes to changes in the rate of formation and subduction of oxygen enriched Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) in the Southern Ocean in association with Atlantic meridional overturning circulation (AMOC) fluctuations (Pichevin et al, 2007;Böning and Bard, 2009). Previous model simulations of the last glaciation confirm that reduced AMOC leads to a reduction in nutrient supply to the Arabian Sea, thus resulting in a decreased productivity and a weakened OMZ (Schmittner et al, 2007).…”

Section: Implications For Paleo-studiesmentioning

confidence: 99%

Intensification and deepening of the Arabian Sea oxygen minimum zone in response to increase in Indian monsoon wind intensity

2018

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Abstract. The decline in oxygen supply to the ocean associated with global warming is expected to expand oxygen minimum zones (OMZs). This global trend can be attenuated or amplified by regional processes. In the Arabian Sea, the world's thickest OMZ is highly vulnerable to changes in the Indian monsoon wind. Evidence from paleorecords and future climate projections indicates strong variations of the Indian monsoon wind intensity over climatic timescales. Yet, the response of the OMZ to these wind changes remains poorly understood and its amplitude and timescale unexplored. Here, we investigate the impacts of perturbations in Indian monsoon wind intensity (from −50 to +50 %) on the size and intensity of the Arabian Sea OMZ, and examine the biogeochemical and ecological implications of these changes. To this end, we conducted a series of eddy-resolving simulations of the Arabian Sea using the Regional Ocean Modeling System (ROMS) coupled to a nitrogen-based nutrient-phytoplankton-zooplanktondetritus (NPZD) ecosystem model that includes a representation of the O 2 cycle. We show that the Arabian Sea productivity increases and its OMZ expands and deepens in response to monsoon wind intensification. These responses are dominated by the perturbation of the summer monsoon wind, whereas the changes in the winter monsoon wind play a secondary role. While the productivity responds quickly and nearly linearly to wind increase (i.e., on a timescale of years), the OMZ response is much slower (i.e., a timescale of decades). Our analysis reveals that the OMZ expansion at depth is driven by increased oxygen biological consumption, whereas its surface weakening is induced by increased ventilation. The enhanced ventilation favors episodic intrusions of oxic waters in the lower epipelagic zone (100-200 m) of the western and central Arabian Sea, leading to intermittent expansions of marine habitats and a more frequent alternation of hypoxic and oxic conditions there. The increased productivity and deepening of the OMZ also lead to a strong intensification of denitrification at depth, resulting in a substantial amplification of fixed nitrogen depletion in the Arabian Sea. We conclude that changes in the Indian monsoon can affect, on longer timescales, the large-scale biogeochemical cycles of nitrogen and carbon, with a positive feedback on climate change in the case of stronger winds. Additional potential changes in large-scale ocean ventilation and stratification may affect the sensitivity of the Arabian Sea OMZ to monsoon intensification.

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“…All these records exhibited very clear signatures of the H-DO events (Pichevin et al 2007;Böning and Bard 2009). …”

Section: A Practical Example-transferring a Timescale From Hulu Cave mentioning

confidence: 94%

Elastic Tie-Pointing—Transferring Chronologies between Records via a Gaussian Process

2013

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ABSTRACT. We consider a general methodology for the transferral of chronologies from a master reference record containing direct dating information to an undated record of interest that does not. Transferral is achieved through the identification, by an expert, of a series of tie-points within both records that are believed to correspond to approximately contemporaneous events. Through tying of the 2 records together at these points, the reference chronology is elastically deformed onto the undated record. The method consists of 3 steps: creation of an age-depth model for the reference record using its direct dating information; selection of the tie-points and translation of their age estimates from the reference to the undated record; and finally, creation of an age-depth model for the undated record using these uncertain tie-point age estimates. Our method takes full account of the uncertainties involved in all stages of the process to create a final chronology within the undated record that allows joint age estimates to be found together with their credible intervals. To achieve computational practicality, we employ a Gaussian process to create our age-depth models. Calculations can then be performed exactly without resort to extremely slow Monte Carlo methods involving multiple independent model fits that would be required by other age-depth models.

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Millennial/centennial-scale thermocline ventilation changes in the Indian Ocean as reflected by aragonite preservation and geochemical variations in Arabian Sea sediments

Cited by 64 publications

References 87 publications

Glacial–interglacial changes and Holocene variations in Arabian Sea denitrification

Glacial–interglacial changes and Holocene variations in Arabian Sea denitrification

Intensification and deepening of the Arabian Sea oxygen minimum zone in response to increase in Indian monsoon wind intensity

Elastic Tie-Pointing—Transferring Chronologies between Records via a Gaussian Process

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