| 1. |
- Fischer, Hubertus, et al.
(author)
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Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond
- 2018
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In: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 11:7, s. 474-485
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Journal article (peer-reviewed)abstract
- Over the past 3.5 million years, there have been several intervals when climate conditions were warmer than during the pre-industrial Holocene. Although past intervals of warming were forced differently than future anthropogenic change, such periods can provide insights into potential future climate impacts and ecosystem feedbacks, especially over centennial-to-millennial timescales that are often not covered by climate model simulations. Our observation-based synthesis of the understanding of past intervals with temperatures within the range of projected future warming suggests that there is a low risk of runaway greenhouse gas feedbacks for global warming of no more than 2 °C. However, substantial regional environmental impacts can occur. A global average warming of 1–2 °C with strong polar amplification has, in the past, been accompanied by significant shifts in climate zones and the spatial distribution of land and ocean ecosystems. Sustained warming at this level has also led to substantial reductions of the Greenland and Antarctic ice sheets, with sea-level increases of at least several metres on millennial timescales. Comparison of palaeo observations with climate model results suggests that, due to the lack of certain feedback processes, model-based climate projections may underestimate long-term warming in response to future radiative forcing by as much as a factor of two, and thus may also underestimate centennial-to-millennial-scale sea-level rise.
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| 2. |
- Schmittner, Andreas, et al.
(author)
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Calibration of the carbon isotope composition (δ13C) of benthic foraminifera
- 2017
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In: Paleoceanography. - 0883-8305. ; 32:6, s. 512-530
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Journal article (peer-reviewed)abstract
- The carbon isotope composition (δ13C) of seawater provides valuable insight on ocean circulation, air-sea exchange, the biological pump, and the global carbon cycle and is reflected by the δ13C of foraminifera tests. Here more than 1700 δ13C observations of the benthic foraminifera genus Cibicides from late Holocene sediments (δ13CCibnat) are compiled and compared with newly updated estimates of the natural (preindustrial) water column δ13C of dissolved inorganic carbon (δ13CDICnat) as part of the international Ocean Circulation and Carbon Cycling (OC3) project. Using selection criteria based on the spatial distance between samples, we find high correlation between δ13CCibnat and δ13CDICnat, confirming earlier work. Regression analyses indicate significant carbonate ion (-2.6 ± 0.4) × 10-3‰/(μmol kg-1) [CO3 2-] and pressure (-4.9 ± 1.7) × 10-3‰ m-1 (depth) effects, which we use to propose a new global calibration for predicting δ13CDICnat from δ13CCibnat. This calibration is shown to remove some systematic regional biases and decrease errors compared with the one-to-one relationship (δ13CDICnat = δ13CCibnat). However, these effects and the error reductions are relatively small, which suggests that most conclusions from previous studies using a one-to-one relationship remain robust. The remaining standard error of the regression is generally σ ≅ 0.25‰, with larger values found in the southeast Atlantic and Antarctic (σ ≅ 0.4‰) and for species other than Cibicides wuellerstorfi. Discussion of species effects and possible sources of the remaining errors may aid future attempts to improve the use of the benthic δ13C record.
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| 3. |
- Vogel, Hendrik, et al.
(author)
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Quantification of biogenic silica by means of Fourier transform infrared spectroscopy (FTIRS) in marine sediments
- 2016
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In: Limnology and Oceanography. - : Wiley-Blackwell. - 1541-5856. ; 14:12, s. 828-838
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Journal article (peer-reviewed)abstract
- Due to the major role played by diatoms in the marine biological pump, opal/biogenic silica (bSi) has a strong potential as a proxy for paleoproduction reconstructions. Here, we present a detailed evaluation of the independent Fourier transform infrared spectroscopy (FTIRS) calibration introduced by Meyer-Jacob et al. (2014a), which is based on synthetic sediment mixtures with known concentrations of bSi and the application of partial least squares (PLS) regression, for the determination of bSi in marine sediments. To test the robustness of the FTIRS calibration for marine samples we selected 199 globally distributed samples, with available wet chemically inferred bSi concentrations and compared the results of both methods. We observe that the spectral characteristics in marine samples are comparable to those reported for a synthetic FTIR spectrum composed solely of spectral features in quartz, biogenic silica, and calcite. FTIRS-inferred and wet-chemically measured bSi concentrations for the set of 199 marine sediment samples are strongly correlated (R-2 = 0.87; RMSE = 5.27%). Together with the high reproducibility of bSi values by the independent calibration our results corroborate the applicability of the independent FTIRS bSi calibration for quantification in marine samples. This together with the succinct sample preparation procedure, rapid analysis, reduced consumable and machine maintenance costs makes FTIRS a powerful and robust alternative for the quantitative analysis of bSi in marine sediments.
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| 4. |
- Zhong, Yi, et al.
(author)
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Orbital Controls on North Pacific Dust Flux During the Late Quaternary
- 2024
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In: Geophysical Research Letters. - 0094-8276. ; 51:4
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Journal article (peer-reviewed)abstract
- Airborne mineral dust is sensitive to climatic changes, but its response to orbital forcing is still not fully understood. Here, we present a reconstruction of dust input to the Subarctic Pacific Ocean covering the past 190 kyr. The dust composition record is indicative of source moisture conditions, which were dominated by precessional variations. In contrast, the dust flux record is dominated by obliquity variations and displays an out-of-phase relationship with a dust record from the mid-latitude North Pacific Ocean. Climate model simulations suggest precession likely drove changes in the aridity and extent of dust source regions. Additionally, the obliquity variations in dust flux can be explained by meridional shifts in the North Pacific westerly jet, driven by changes in the meridional atmospheric temperature gradient. Overall, our findings suggest that North Pacific dust input was primarily modulated by orbital-controlled source aridity and the strength and position of the westerly winds.
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