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  • 1
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    Calcium isotopic composition of high-latitude proxy carrier Neogloboquadrina pachyderma (sin.) (2009)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 6 (1). pp. 1-14.
    Details
    Publication Date: 2012-07-06
    Description: The accurate reconstruction of sea surface temperature (SST) history in climate-sensitive regions (e.g. tropical and polar oceans) became a challenging task in palaeoceanographic research. Biogenic shell carbonate SST proxies successfully developed for tropical regions often fail in cool water environments. Their major regional shortcomings and the cryptic diversity now found within the major high latitude proxy carrier Neogloboquadrina pachyderma (sin.) highlight an urgent need to explore complementary SST proxies for these cool-water regions. Here we incorporate the genetic component into a calibration study of a new SST proxy for the high latitudes. We found that the calcium isotopic composition (δ44/40Ca) of calcite from genotyped net catches and core-top samples of the planktonic foraminifera Neogloboquadrina pachyderma (sin.) is related to temperature and unaffected by genetic variations. The temperature sensitivity has been found to be 0.17 (±0.02)‰ per 1°C, highlighting its potential for downcore applications in open marine cool-water environments. Our results further indicate that in extreme polar environments, below a critical threshold temperature of 2.0 (±0.5)°C associated with salinities below 33.0 (±0.5)‰, a prominent shift in biomineralization affects the δ44/40Ca of genotyped and core-top N. pachyderma (sin.), becoming insensitive to temperature. These findings highlight the need of more systematic calibration studies on single planktonic foraminiferal species in order to unravel species-specific factors influencing the temperature sensitivity of Ca isotope fractionation and to validate the proxies' applicability.
    Type: Article , PeerReviewed
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  • 2
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    The DeepMIP contribution to PMIP4: methodologies for selection, compilation and analysis of latest Paleocene and early Eocene climate proxy data, incorporating version 0.1 of the DeepMIP database (2019)
    Copernicus Publications (EGU)
    In:  Geoscientific Model Development, 12 (7). pp. 3149-3206.
    Details
    Publication Date: 2022-01-31
    Description: The early Eocene (56 to 48 million years ago) is inferred to have been the most recent time that Earth's atmospheric CO2 concentrations exceeded 1000 ppm. Global mean temperatures were also substantially warmer than present day. As such, study of early Eocene climate provides insight into how a super-warm Earth system behaves and offers an opportunity to 10 evaluate climate models under conditions of high greenhouse gas forcing. The Deep Time Model Intercomparison Project (DeepMIP) is a systematic model-model and model-data intercomparison of three early Paleogene time slices: latest Paleocene, Paleocene-Eocene thermal maximum and early Eocene climatic optimum. A previous article outlined the model experimental design for climate model simulations. In this article, we outline the methodologies to be used for the compilation and analysis of climate proxy data, primarily proxies for temperature and CO2. This paper establishes the protocols for a concerted and 15 coordinated effort to compile the climate proxy records across a wide geographic range. The resulting climate "atlas" will be used to constrain and evaluate climate models for the three selected time intervals, and provide insights into the mechanisms that control these warm climate states. We provide version 0.1 of this database, in anticipation that this will be expanded in subsequent publications.
    Type: Article , PeerReviewed
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  • 3
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    delta 44/40Ca, Mg/Ca and delta 18O ratios of planktonic foraminifera from the Nordic Seas (2007)
    Details
    Publication Date: 2023-01-06
    Description: A new approach for a solid delta44/40Ca temperature calibration of the polar to subpolar planktonic foraminifera N. pachyderma (sin.) is presented, based on a broad sample pool comprising North and South Atlantic genotyped net catches and Nordic Seas core top sample material. With this new additional SST proxy, the 'cold end' error of proxy temperature calibrations was addressed in combining delta44/40Ca, Mg/Ca and delta18O ratios in tests of N. pachyderma (sin.). At water temperatures below about 3.5°C, the proxy to temperature relationship recorded in the Mg/Ca and delta44/40Ca signal simultaneously disappears. Based on these 'cold-end' proxy-data we present a model demonstrating that the aberrant delta44/40Ca and Mg/Ca ratios in N. pachyderma (sin.) calcified in cold polar waters can be interpreted by a two-step chemical modification of vacuolized seawater during its cytosolar transport to the calcification site.
    Type: Thesis , NonPeerReviewed
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  • 4
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    High‐resolution Mg/Ca and δ 18 O patterns in modern Neogloboquadrina pachyderma from the Fram Strait and Irminger Sea (2020)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2023-02-08
    Description: Neogloboquadrina pachyderma is the dominant species of planktonic foraminifera found in polar waters and is therefore invaluable for paleoceanographic studies of the high latitudes. However, the geochemistry of this species is complicated due to the development of a thick calcite crust in its final growth stage and at greater depths within the water column. We analyzed the in situ Mg/Ca and δ18O in discrete calcite zones using LA‐ICP‐MS, EPMA and SIMS within modern N. pachyderma shells from the highly dynamic Fram Strait and the seasonally isothermal/isohaline Irminger Sea. Here we compare shell geochemistry to the measured temperature, salinity and δ18Osw in which the shells calcified to better understand the controls on N. pachyderma geochemical heterogeneity. We present a relationship between Mg/Ca and temperature in N. pachyderma lamellar calcite that is significantly different than published equations for shells that contained both crust and lamellar calcite. We also document highly variable SIMS δ18O results (up to a 3.3‰ range in single shells) on plankton tow samples which we hypothesize is due to the granular texture of shell walls. Finally, we document that the δ18O of the crust and lamellar calcite of N. pachyderma from an isothermal/isohaline environment are indistinguishable from each other, indicating that shifts in N. pachyderma δ18O are primarily controlled by changes in environmental temperature and/or salinity rather than differences in the sensitivities of the two calcite types to environmental conditions.
    Type: Article , PeerReviewed
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