| 1. |
- Kaboth-Bahr, Stefanie, et al.
(författare)
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Deciphering similar to 45.000 years of Arctic Ocean lithostratigraphic variability through multivariate statistical analysis
- 2019
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Ingår i: Quaternary International. - : Elsevier BV. - 1040-6182 .- 1873-4553. ; 514, s. 141-151
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Tidskriftsartikel (refereegranskat)abstract
- Our understanding of past climate conditions in the Arctic Ocean has been hampered by poor age control caused in part by low sedimentation rates (< 1 cm/kyr), hiatuses during glacial intervals as well as the scarcity and poor preservation of calcareous nanno-and microfossils in the sediments. Although recent advances using variations in single element (e.g. Mn) content or physical sediment properties (e.g. bulk density, grain size, colour) of the recovered sediments have aided Arctic core-to-core correlations, unique depositional events and post-depositional changes can complicate stratigraphic interpretations based on individual or even multiple, physical or chemical parameters. Furthermore, clear correlations between cores using physical and chemical parameters are not always possible to establish. To tackle this issue, we developed an algorithm that combines clustering and multivariate ordination to test the interrelation of multiple input parameters (e.g. an array of individual XRF elemental contents), and subsequently identifies statistically significant stratigraphic units on centimetre to decimetre scales. Our preliminary results show that a distinct sedimentological pattern during the past 45,000 years characterizes cores from the region of the Morris Jesup Rise and the Greenland side of the Lomonosov Ridge. Stratigraphic patterns of the Siberian Side of the Lomonosov Ridge yield distinct differences, thus allowing for novel insights into sedimentary processes shaping the different regions within the Arctic Ocean. We also argue that our approach can compensate for some of the weakness of single element or proxy applications, and hence aid the construction of a robust stratigraphic framework for a wide geographical range of Arctic Ocean sediments.
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| 2. |
- O'Regan, Matt, et al.
(författare)
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Stratigraphic Occurrences of Sub-Polar Planktic Foraminifera in Pleistocene Sediments on the Lomonosov Ridge, Arctic Ocean
- 2019
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Ingår i: Frontiers in Earth Science. - : FRONTIERS MEDIA SA. - 2296-6463. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Turborotalita quinqueloba is a species of planktic foraminifera commonly found in the sub-polar North Atlantic along the pathway of Atlantic waters in the Nordic seas and sometimes even in the Arctic Ocean, although its occurrence there remains poorly understood. Existing data show that T. quinqueloba is scarce in Holocene sediments from the central Arctic but abundance levels increase in sediments from the last interglacial period [Marine isotope stage (MIS) 5, 71-120 ka] in cores off the northern coast of Greenland and the southern Mendeleev Ridge. Turborotalita also occurs in earlier Pleistocene interglacials in these regions, with a unique and widespread occurrence of the less known Turborotalita egelida morphotype, proposed as a biostratigraphic marker for MIS 11 (474-374 ka). Here we present results from six new sediment cores, extending from the central to western Lomonosov Ridge, that show a consistent Pleistocene stratigraphy over 575 km. Preliminary semi-quantitative assessments of planktic foraminifer abundance and assemblage composition in two of these records (LOMROG12-7PC and AO16-5PC) reveal two distinct stratigraphic horizons containing Turborotalita in MIS 5. Earlier occurrences in Pleistocene interglacials are recognized, but contain significantly fewer specimens and do not appear to be stratigraphically coeval in the studied sequences. In all instances, the Turborotalita specimens resemble the typical T. quinqueloba morphotype but are smaller (63-125 mu m), smooth-walled and lack the final thickened calcite layer common to adults of the species. These results extend the geographical range for T. quinqueloba in MIS 5 sediments of the Arctic Ocean and provide compelling evidence for recurrent invasions during Pleistocene interglacials.
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| 3. |
- Yamoah, Kweku A., et al.
(författare)
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A muted El Nino-like condition during late MIS 3
- 2021
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 254
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Tidskriftsartikel (refereegranskat)abstract
- The evolutionary dynamics of El Nino Southern Oscillation (ENSO) over the last glacial period remains understudied, despite its potential in providing a cold case for climate sensitivity studies. Here, we investigate SE Asian-Pacific paleoclimate records to decipher the dominant underlying mechanism that governed tropical Asian-Pacific hydrology during MIS 3. Our results suggest that the glacial emergence of the Sunda Shelf likely altered the atmospheric circulation pattern in Southeast (SE) Asia and led to the realignment of rainfall patterns between Thailand and Indonesia during the last glacial period. We also propose that the long-term hydrological regime change in the tropical Asian-Pacific region during MIS 3 was mainly influenced by an El Nino-like mechanism. An intense El Nino-like condition led to strong aridity in SE Asia during mid MIS 3. By late MIS 3, an enhanced seasonality dampened the intensity of the El Nino-like conditions, thus, leading to muted aridity in SE Asia. The alternating warm and wet summer months and droughts during winter favoured the proliferation of C4 plant types in Northern Thailand from mid MIS 3 to late MIS 3.
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| 4. |
- Zhong, Yi, et al.
(författare)
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Humidification of Central Asia and equatorward shifts of westerly winds since the late Pliocene
- 2022
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Ingår i: Communications Earth and Environment. - : Springer Science and Business Media LLC. - 2662-4435. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- The production, transport, and deposition of mineral dust exert major influences on climate change and Earth’s biogeochemical cycles. Furthermore, their imprint, as recorded in pelagic sediments, provides an avenue for determining past changes in terrestrial aridity and atmospheric circulation patterns in response to global climate change. Here, by examining geochemical and magnetic data obtained from a ferromanganese crust in the western Pacific Ocean, we investigate the eolian dust source-region conditions and dust transport mechanisms from the Asian interior to the Pacific Ocean since the Pliocene. We identify a gradual provenance change in the dust source regions, from a dominant Gobi Desert source during the early Pliocene to a mixed Gobi-Taklimakan Desert source during the late Pliocene and Pleistocene, alongside increasing chemical weathering in those source areas. Climate model simulations suggest that these changes were related to an equatorward shift of the westerly jet and humidification of Central Asia during the gradual transition from a warm Pliocene climate to the cool Pleistocene.
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| 5. |
- Zhong, Yi, et al.
(författare)
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Orbital Controls on North Pacific Dust Flux During the Late Quaternary
- 2024
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Ingår i: Geophysical Research Letters. - 0094-8276. ; 51:4
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Tidskriftsartikel (refereegranskat)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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