Deciphering the Modern Calcification Depth of Globigerina Bulloides in the Southwestern Indian Ocean From Its Oxygen Isotopic Composition

Saraswat, Rajeev; Khare, Neloy

doi:10.2113/gsjfr.40.3.220

Cited by 11 publications

(6 citation statements)

References 38 publications

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“…Planktic foraminifera G. bulloides inhabits the water above the thermocline at around 75 to 100 m 51 52 . The thermocline in the Indian sector of Southern Ocean is known to vary within the range of 75−150 m 53 .…”

Section: Resultsmentioning

confidence: 99%

Isotopic disequilibrium in Globigerina bulloides and carbon isotope response to productivity increase in Southern Ocean

Prasanna

Ghosh

Bhattacharya

et al. 2016

Sci Rep

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Oxygen and carbon isotope ratios in planktonic foraminifera Globigerina bulloides collected from tow samples along a transect from the equatorial Indian ocean to the Southern Ocean (45°E and 80°E and 10°N to 53°S) were analysed and compared with the equilibrium δ18O and δ13C values of calcite calculated using the temperature and isotopic composition of the water column. The results agree within ~0.25‰ for the region between 10°N and 40°S and 75–200 m water depth which is considered to be the habitat of Globigerina bulloides. Further south (from 40°S to 55°S), however, the measured δ18O and δ13C values are higher than the expected values by ~2‰ and ~1‰ respectively. These enrichments can be attributed to either a ‘vital effect’ or a higher calcification rate. An interesting pattern of increase in the δ13C(DIC) value of the surface water with latitude is observed between 35°S and~ 60°S, with a peak at~ 42°S. This can be caused by increased organic matter production and associated removal. A simple model accounting for the increase in the δ13C(DIC) values is proposed which fits well with the observed chlorophyll abundance as a function of latitude.

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Section: Resultsmentioning

confidence: 99%

Isotopic disequilibrium in Globigerina bulloides and carbon isotope response to productivity increase in Southern Ocean

Prasanna

Ghosh

Bhattacharya

et al. 2016

Sci Rep

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“…4 is ±3 °C). Recent core-top sediments studies carried out in the Southwest Pacific Ocean (33–54°S) have shown that temperature reconstructions obtained with Mg/Ca on G. bulloides correlates best with water temperatures at 200 m depth 80 .…”

Section: Methodsmentioning

confidence: 99%

Southern Ocean warming and Wilkes Land ice sheet retreat during the mid-Miocene

et al. 2018

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Observations and model experiments highlight the importance of ocean heat in forcing ice sheet retreat during the present and geological past, but past ocean temperature data are virtually missing in ice sheet proximal locations. Here we document paleoceanographic conditions and the (in)stability of the Wilkes Land subglacial basin (East Antarctica) during the mid-Miocene (~17–13.4 million years ago) by studying sediment cores from offshore Adélie Coast. Inland retreat of the ice sheet, temperate vegetation, and warm oligotrophic waters characterise the mid-Miocene Climatic Optimum (MCO; 17–14.8 Ma). After the MCO, expansion of a marine-based ice sheet occurs, but remains sensitive to melting upon episodic warm water incursions. Our results suggest that the mid-Miocene latitudinal temperature gradient across the Southern Ocean never resembled that of the present day. We demonstrate that a strong coupling of oceanic climate and Antarctic continental conditions existed and that the East Antarctic subglacial basins were highly sensitive to ocean warming.

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“…Hemleben et al (1989) suggest a depth above 400m, but more specifically above the thermocline. Other studies such as Saraswat and Khare (2010) and Niebler et al (1999) are in agreement with Hemleben et al (1989) with estimates of 0-200m and 0-100m, respectively. This species is constrained by sea surface temperatures of 0 to 27 C with peak abundance occurring between 3 and 19 C (Bé and Tolderlund, 1971).…”

Section: Introductionsupporting

confidence: 78%

Impact of large volcanic events on the marine environment recorded in marine cores

Wilkinson¹

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<p>Explosive silicic volcanic eruptions blanket widespread terrestrial and marine areas in ash, and have a profound effect on climate and local ecosystems. Short-term climate effects are caused by the dispersal of ash, but the injection of gas into the stratosphere, with sulphur being particularly important, drives a cooling of the climate that can last several years. These prolonged perturbations have been observed and recorded in recent decades, but despite the importance of the ocean in regulating global atmospheric climate, little is known about how and to what extent the climate signal produced by volcanic eruptions alters the oceanic environment. As the composition of foraminifera tests is highly sensitive to changes in the surrounding environment, a significant sea surface temperature decrease following a large silicic volcanic eruption may be recorded in the tests of live planktic foraminifera, now preserved in marine sediments. This study examines marine cores (and foraminifera within) that contain tephra units from three major volcanic events to determine if changes can be resolved in ocean temperature and/or foraminifera test morphology following large silicic eruptions. The Holocene Taupo, Waimihia and Mamaku tephra units have been identified in a series of marine sediment cores collected from areas with high sedimentation rates off the east coast of North Island, New Zealand. The sources of these eruptions were from two calderas within the Taupo Volcanic Zone, one of the most active and important rhyolitic regions in the world. Sampling of sediment and foraminifera from these cores has been undertaken at 0.5 cm intervals above and below each tephra. This equates to varying sampling resolutions between cores of 5-30 years, with sufficient sampling taken to establish a stratigraphic record of >100 years either side of each tephra unit. A detailed stratigraphy was undertaken on the sediment surrounding all tephra units, including grain size and CaCO₃ analyses, to identify primary and secondary tephra deposits. One core, Tan0810-12 that contained solely Taupo tephra, was selected for foraminiferal analyses to determine changes in ocean temperature and foraminifera test morphology following this eruption. This core was selected based on the results of the stratigraphic analyses that identified the tephra as a primary deposit with minimal bioturbation above the ash layer and a very high sedimentation rate that enabled sub-decadal scale sampling. Scanning electron microscope imaging was employed to identify the presence of surface contaminants on and within the foraminifera tests and allowed observations of test morphology and size. The morphologies of planktic foraminifera species Globigerinoides ruber and Globigerina bulloides showed no obvious change following the Taupo eruption. The Globigerinoides ruber test sizes distinctly decreased for a period after the eruption, while Globigerina bulloides tests slightly increased in size, correlating well with a decrease in sea surface temperature after the eruption as these species prefer warmer and colder temperatures, respectively. This suggests there is potential for test size to be employed as a proxy for temperature change in conjunction with geochemical analyses. Mg/Ca temperature analyses were conducted in situ using laser ablation inductively coupled plasma mass spectrometry. Both species indicated a decrease in sea surface temperatures when comparing results from tests collected below the tephra deposit to those above. Further results indicate ocean temperature may not have recovered for more than 65 years after the eruption. Such a rapid change in the oceanic environment not only has drastic implications for marine ecosystems but also atmospheric climate, and therefore, terrestrial ecosystems. To reduce the margin of error and determine a more exact value of temperature change following the eruption a greater population of foraminifera is needed. Nonetheless, this study highlights the potential of this method in determining how the oceans are impacted by volcanism and how further research is needed to determine the effects of volcanic eruptions on past and future climate.</p>

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Deciphering the Modern Calcification Depth of Globigerina Bulloides in the Southwestern Indian Ocean From Its Oxygen Isotopic Composition

Cited by 11 publications

References 38 publications

Isotopic disequilibrium in Globigerina bulloides and carbon isotope response to productivity increase in Southern Ocean

Isotopic disequilibrium in Globigerina bulloides and carbon isotope response to productivity increase in Southern Ocean

Southern Ocean warming and Wilkes Land ice sheet retreat during the mid-Miocene

Impact of large volcanic events on the marine environment recorded in marine cores

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