Causes and climatic influence of centennial-scale denitrification variability in the southeastern Arabian Sea since the last glacial period

2021 ◽  
pp. 1-13
Author(s):  
Sidhesh Nagoji ◽  
Manish Tiwari
Keyword(s):  
Arabian Sea ◽  
Asian Summer Monsoon ◽  
Intermediate Water ◽  
Glacial Period ◽  
South Asian Summer Monsoon ◽  
Last Glacial Period ◽  
The Holocene ◽  
Last Glacial ◽  
Southeastern Arabian Sea ◽  
The Last Glacial

Abstract Denitrification occurring in the oxygen minimum zone of the Arabian Sea produces nitrous oxide, a powerful greenhouse gas. Therefore, it is important to understand the mechanisms controlling denitrification's intensity and evaluate its influence on the global climate at various timescales. We studied multiple geochemical and isotopic proxies in a sediment core from the southeastern Arabian Sea (SEAS) at a high (centennial-scale) resolution. We find that since the last glacial period, both the ventilation and the productivity caused by the South Asian summer monsoon played a major role in controlling the denitrification variability in SEAS. During the Last Glacial Maximum (LGM) and since the Holocene, denitrification increased in SEAS despite reduced monsoon-induced productivity. During the LGM, weakened thermohaline circulation resulted in reduced ventilation of the intermediate waters of SEAS, causing increased denitrification. During the Holocene, the increase in denitrification is caused by an enhanced inflow of oxygen-depleted Red Sea and Persian Gulf waters into the intermediate depth of SEAS owing to a rising sea level that prohibited ventilation by the Antarctic Intermediate Water. We further find millennial-scale synchronicity between denitrification in SEAS, global monsoons, and the North Atlantic climate, implying systematic linkages via greenhouse gases abundance.

Contrasting Patterns in Abrupt Asian Summer Monsoon Changes in the Last Glacial Period and the Holocene

2018 ◽  
Vol 33 (2) ◽  
pp. 214-226 ◽  
Author(s):  
Dianbing Liu ◽  
Yongjin Wang ◽  
Hai Cheng ◽  
R. L. Edwards ◽  
Xinggong Kong ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Glacial Period ◽  
Last Glacial Period ◽  
The Holocene ◽  
Last Glacial ◽  
Asian Summer ◽  
The Last Glacial

LONG-TERM RATES OF FAULTING DERIVED FROM COSMOGENIC NUCLIDES AND SHORT-TERM VARIATIONS CAUSED BY GLACIAL-INTERGLACIAL VOLUME CHANGES OF GLACIERS AND LAKES

2006 ◽  
Vol 20 (03) ◽  
pp. 261-276 ◽  
Author(s):  
RALF HETZEL ◽  
ANDREA HAMPEL
Keyword(s):  
Slip Rate ◽  
Alluvial Fan ◽  
Glacial Period ◽  
Last Glacial Period ◽  
Slip Rates ◽  
The Holocene ◽  
Last Glacial ◽  
River Terraces ◽  
The Last Glacial

Seismic hazard evaluations on major faults in Earth's crust are based on their slip histories, which reflect the frequency of earthquakes that ruptured a fault in the past. On a 100 000-year timescale, the slip rate of a fault can be determined by dating geomorphic surfaces that are offset by a fault. Application of this method to alluvial fan surfaces and river terraces offset by thrust faults in Tibet yields long-term slip rates of less than 1mm/a. Slip rates on a 10 000-year timescale are derived from paleoseismologic data and document that faults experience considerable slip rate variations on timescales of 100 to 1000 years. In particular, slip rates are often considerable higher in the present interglacial, the Holocene, than during the last glacial period, the Late Pleistocene. The causes of this behavior have remained enigmatic but their assessment is essential for an accurate evaluation of a fault's past and future seismicity. Numerical experiments show that the retreat of lakes and glaciers at the end of the last glacial period can cause an increase in the Holocene slip rate of a fault. Such a correlation between enhanced seismicity and climate-driven mass fluctuations on Earth's surface is best documented for the Wasatch Fault, Utah.

scholarly journals Southern Hemisphere imprint for Indo-Asian summer monsoons during the last glacial period as revealed by Arabian Sea productivity records

2013 ◽  
Vol 10 (11) ◽  
pp. 7347-7359 ◽  
Author(s):  
T. Caley ◽  
S. Zaragosi ◽  
J. Bourget ◽  
P. Martinez ◽  
B. Malaizé ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Arabian Sea ◽  
Asian Monsoon ◽  
Glacial Period ◽  
Last Glacial Period ◽  
Last Glacial ◽  
Asian Summer ◽  
Asian Monsoons ◽  
The Last Glacial

Abstract. The monsoon is one of the most important climatic phenomena: it promotes inter-hemispheric exchange of energy and affects the economical prosperity of several countries exposed to its seasonal seesaw. Previous studies in both the Indian and Asian monsoon systems have generally suggested a dominant northern hemispheric (NH) control on summer monsoon dynamics at the scale of suborbital–millennial climatic changes, while the forcing/response of Indian and Asian monsoons at the orbital scale remains a matter of debate. Here, six marine sediment cores distributed across the whole Arabian Sea are used to build a regional surface marine productivity signal. The productivity signal is driven by the intensity of Indian summer monsoon winds. Our results demonstrate the existence of an imprint of suborbital southern hemispheric (SH) temperature changes (i.e. Antarctica) on the Indian summer monsoon during the last glacial period that is generally not recognized. During the last deglaciation, the NH played a more significant role. This suggests that fluctuations in the Indian monsoon are better explained in a bipolar context. The δ18O signal recorded in the Asian monsoon speleothem records could be exported by winds from the Indian summer monsoon region, as recently proposed in modelling exercise, explaining the SH signature observed in Asian cave speleothems. Contrary to the view of a passive response of Indian and Asian monsoons to NH anomalies, the present results appear to suggest that the Indo-Asian summer monsoon plays an active role in amplifying millennial inter-hemispheric asymmetric patterns. Additionally, this study confirms previously observed differences between Indian and Asian speleothem monsoonal records at the orbital-precession scale.

scholarly journals Abrupt sea surface pH change at the end of the Younger Dryas in the central sub-equatorial Pacific inferred from boron isotope abundance in corals (<i>Porites</i>)

2010 ◽  
Vol 7 (2) ◽  
pp. 1959-1993 ◽  
Author(s):  
E. Douville ◽  
M. Paterne ◽  
G. Cabioch ◽  
P. Louvat ◽  
J. Gaillardet ◽  
...  
Keyword(s):  
Younger Dryas ◽  
Equatorial Pacific ◽  
Sea Surface ◽  
Glacial Period ◽  
Ph Change ◽  
Last Glacial Period ◽  
Surface Ph ◽  
The Holocene ◽  
Last Glacial ◽  
The Last Glacial

Abstract. The "δ11B-pH" technique was applied to modern and ancient Porites from the sub-equatorial Pacific areas (Tahiti and Marquesas) spanning a time interval from 0 to 20 720 calendar years to determine the amplitude of pH changes between the Last Glacial Period and the Holocene. Boron isotopes were measured by Multi-Collector-Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) with an external reproducibility of 0.25‰, allowing a precision of ±0.025 pH-units. The boron concentration [B] and isotopic composition of modern samples indicate that the temperature strongly controls the partition coefficient KD for different aragonite species. Modern coral δ11B values and the reconstructed sea surface pH values for different Pacific areas match the measured pH expressed on the Sea Water Scale and confirm the calculation parameters that were previously determined by laboratory calibration exercises. Most ancient sea surface pH reconstructions near Marquesas are higher than modern values. These values range between 8.20 and 8.26 for the Holocene and reached 8.31 at the end of the last glacial period (20.7 kyr BP). At the end of the Younger Dryas (11.50±0.1 kyr BP), the central sub-equatorial Pacific experienced a dramatic drop of up to 0.2 pH-units from the average pH of 8.2 before and after this short event. Using the CO2SYS program, we recalculated the aqueous pCO2 to be 400±24 ppmV at around 11.5 kyr BP for corals at Marquesas and ~500 ppmV near Tahiti where it was assumed that pCO2 in the atmosphere was 250 ppmV. Throughout the Holocene, the difference in pCO2 between the ocean and the atmosphere at Marquesas (ΔpCO2) indicates that the surface waters behave as a moderate CO2 sink (−67 to −11 ppmV) during El Niño-like conditions. In contrast, during the last glacial/interglacial transition, this area was a moderate source of CO2 (−9 to 56 ppmV) for the atmosphere, highlighting predominant La Niña-like conditions. Such conditions were particularly pronounced at the end of the Younger Dryas with a large amount of CO2 released with ΔpCO2 of +140 ppmV. This last finding provides further evidence of the marked changes to the water mass pH and temperature properties in the equatorial Pacific at the Younger Dryas- Holocene transition and the strong impact of oceanic dynamic on the atmospheric CO2 content.

scholarly journals Abrupt sea surface pH change at the end of the Younger Dryas in the central sub-equatorial Pacific inferred from boron isotope abundance in corals (<i>Porites</i>)

2010 ◽  
Vol 7 (8) ◽  
pp. 2445-2459 ◽  
Author(s):  
E. Douville ◽  
M. Paterne ◽  
G. Cabioch ◽  
P. Louvat ◽  
J. Gaillardet ◽  
...  
Keyword(s):  
Younger Dryas ◽  
Equatorial Pacific ◽  
Sea Surface ◽  
Glacial Period ◽  
Last Glacial Period ◽  
Surface Ph ◽  
The Holocene ◽  
Last Glacial ◽  
Ph Values ◽  
The Last Glacial

Abstract. The "δ11B-pH" technique was applied to modern and ancient corals Porites from the sub-equatorial Pacific areas (Tahiti and Marquesas) spanning a time interval from 0 to 20.720 calendar years to determine the amplitude of pH changes between the Last Glacial Period and the Holocene. Boron isotopes were measured by Multi-Collector – Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) with an external reproducibility of 0.25‰, allowing a precision of about ±0.03 pH-units for pH values between 8 and 8.3. The boron concentration [B] and isotopic composition of modern samples indicate that the temperature strongly controls the partition coefficient KD for different aragonite species. Modern coral δ11B values and the reconstructed sea surface pH values for different Pacific areas match the measured pH expressed on the seawater scale and confirm the calculation parameters that were previously determined by laboratory calibration exercises. Most ancient sea surface pH reconstructions near Marquesas are higher than modern values. These values range between 8.19 and 8.27 for the Holocene and reached 8.30 at the end of the last glacial period (20.7 kyr BP). At the end of the Younger Dryas (11.50±0.1 kyr BP), the central sub-equatorial Pacific experienced a dramatic drop of up to 0.2 pH-units from the average pH of 8.2 before and after this short event. Using the marine carbonate algorithms, we recalculated the aqueous pCO2 to be 440±25 ppmV at around 11.5 kyr BP for corals at Marquesas and ~500 ppmV near Tahiti where it was assumed that pCO2 in the atmosphere was 250 ppmV. Throughout the Holocene, the difference in pCO2 between the ocean and the atmosphere at Marquesas (ΔpCO2) indicates that the surface waters behave as a moderate CO2 sink or source (−53 to 20 ppmV) during El Niño-like conditions. By contrast, during the last glacial/interglacial transition, this area was a marked source of CO2 (21 to 92 ppmV) for the atmosphere, highlighting predominant La Niña-like conditions. Such conditions were particularly pronounced at the end of the Younger Dryas with a large amount of CO2 released with ΔpCO2 of +185±25 ppmV. This last finding provides further evidence of the marked changes in the surface water pH and temperature in the equatorial Pacific at the Younger Dryas-Holocene transition and the strong impact of oceanic dynamic on the atmospheric CO2 content.

Fragilariopsis kerguelensis size variability from the Indian subtropical Southern Ocean over the last 42 000 years

2016 ◽  
Vol 29 (2) ◽  
pp. 139-146 ◽  
Author(s):  
Sunil Kumar Shukla ◽  
Xavier Crosta
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Glacial Period ◽  
Last Glacial Period ◽  
Subtropical Zone ◽  
The Holocene ◽  
Last Glacial ◽  
Size Variability ◽  
The Last Glacial ◽  
Valve Area

AbstractIn the open Southern Ocean (SO), both modern and past size changes of the diatom Fragilariopsis kerguelensis appear to be strongly controlled by iron availability. Conversely, sea surface temperatures (SST) and sea ice seasonal dynamics take over in the seasonal sea-ice zone where iron is not limiting. No information exists on F. kerguelensis biometry from the subtropical SO, on the other extreme of the thermal and nutrient gradients. We present here new data on mean valve area of F. kerguelensis (FkergArea) from a sediment core covering the last ~42 cal kyrs from the southern Subtropical Front (SSTF) of the Indian sector of the SO, where iron and silica stocks are thought to have been consistently low over this period. Our results suggest that larger F. kerguelensis valves occurred during the Last Glacial period, and declined during the Holocene period. These findings indicate that more favourable SST, within the F. kerguelensis ecological range, during the Last Glacial period may have enabled F. kerguelensis to make better use of the low silica stocks prevailing in the subtropical zone leading to larger valves. Conversely, declining FkergArea during the deglacial and the Holocene periods may have been a result of higher SST which hampered the utilization of silica.

scholarly journals Mineralogical Record for Stepwise Hydroclimatic Changes in Lake Qinghai Sediments Since the Last Glacial Period

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 963
Author(s):  
Yougui Song ◽  
Xiulan Zong ◽  
Linbo Qian ◽  
Huifang Liu ◽  
Jibao Dong ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Lake Level ◽  
East Asian Monsoon ◽  
Asian Summer Monsoon ◽  
Glacial Period ◽  
Lake Qinghai ◽  
Last Glacial Period ◽  
Last Glacial ◽  
Mineral Assemblages ◽  
The Last Glacial

Lake Qinghai is sensitive to climatic changes because of its pivotal location between mid-latitude Westerlies and the low-latitude East Asian monsoon. An 18.6 m long drilling core (1Fs) from Lake Qinghai provides new information on the hydroclimatic dynamics since the last glacial period. Here, we present the results of bulk mineral assemblages of this core. X-ray diffraction (XRD) results showed that the bulk minerals of the core sediments consist of major clastic minerals (e.g., quartz, feldspar, muscovite), carbonates (e.g., calcite, aragonite, dolomite), and minor clay minerals (e.g., chlorite). Quartz as an exogenous detrital mineral in lake sediments, its abundance is related to lake level changes resulting from regional climate changes via fluvial/aeolian transportation. Aragonite was precipitated from water solutions or chemical alteration of pre-existing minerals or biogenic mediation, closely related to lake hydroclimate change. Mineral assemblages revealed remarkable stepwise hydroclimatic changes. High quartz content and low calcite without aragonite suggested a cold-wet climate condition under predominant westerlies during the last glacial period from 35 to 25.3 ka. Afterward, quartz decreased and aragonite occasionally appeared, indicating an unstable hydroclimatic condition during the last deglaciation. Since the Early Holocene (11.9–8.2 ka), predominant minerals shifted from terrigenous quartz to authigenic carbonates, suggesting an increasing lake level, possibly due to intensified Asian summer monsoon with increased effective moisture. Aragonite became the primary carbonate mineral, implying a warming and humid hydroclimate environment with a relatively higher lake-level. During the Middle Holocene (8.2–4.2 ka), aragonite showed a decreasing trend indicating a higher lake level with weak evaporation. During the Late Holocene since 4.2 ka, there were lower quartz and aragonite, suggesting a deep lake with a weak summer monsoon. Our quartz and carbonate minerals record provided essential clues to reconstruct hydroclimate change in Lake Qinghai since the last glacial period.

scholarly journals How Ice Rafting Events Affect Asian Monsoon Hydroclimate

Eos ◽  
2018 ◽  
Vol 99 ◽  
Author(s):  
Sarah Stanley
Keyword(s):  
Asian Monsoon ◽  
Glacial Period ◽  
Last Glacial Period ◽  
The Holocene ◽  
Isotopic Evidence ◽  
Last Glacial ◽  
Heinrich Events ◽  
Ice Rafting ◽  
The Last Glacial

Cave stalagmites provide isotopic evidence that Bond events and Heinrich events have more variable effects on Asian monsoon hydroclimate during the last glacial period than during the Holocene.

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