| 1. |
- Moros, M, et al.
(författare)
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Quartz content and the quartz-to-plagioclase ratio determined by X-ray diffraction: a proxy for ice rafting in the northern North Atlantic?
- 2004
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Ingår i: Earth and Planetary Science Letters. - 1385-013X. ; 218:3-4, s. 389-401
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Tidskriftsartikel (refereegranskat)abstract
- Many paleoceanographic reconstructions of the glacial North Atlantic include estimates of iceberg discharge, which are based on the variable abundance of ice-rafted detritus (IRD) in deep-sea sediments. IRD abundance is most often determined by the mechanical separation and painstaking counting of terrigenous particles larger than a specified threshold grain size, typically 150 mum. Here we present a new proxy for IRD based on X-ray diffraction (XRD) analysis of bulk sediments. This approach complements results obtained from standard techniques while offering several distinct advantages. In addition to the rapid production of objective data, XRD measurements on bulk sediments are sensitive to a broader and more characteristic grain size range than counts of individual coarse lithic fragments. The technique is demonstrated in a study of 12 sediment cores from the North Atlantic. Bulk quartz content and the quartz-to-plagioclase ratio exhibit peak-to-peak correspondence to manual counting results, which verifies the identification of large IRD influxes. The XRD data also reveal variations between the manually identified peaks, suggesting increased sensitivity to low-level, distal, or sea-ice sources of IRD. A saw-tooth pattern emerges in many IRD events, which supports a link between ice rafting and atmospheric temperature changes over Greenland, and providing further evidence of the influence of climate on iceberg discharges. (C) 2003 Elsevier B.V. All rights reserved.
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| 2. |
- Moros, M, et al.
(författare)
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Sea surface temperatures and ice rafting in the Holocene North Atlantic: climate influences on Northern Europe and Greenland
- 2004
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 23:20-22, s. 2113-2126
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Tidskriftsartikel (refereegranskat)abstract
- The oceanographic conditions in the high-latitude North Atlantic ocean during the Holocene were reconstructed through analyses of sea surface temperature (SST; alkenone unsaturation ratios) and ice rafting (mineralogy and grain size) from two sediment sequences, one recovered from the Reykjanes Ridge at 59degreesN and the other from the Norwegian Sea at 68degreesN. Comparison of our records to published ice core and terrestrial proxy-climate data sets suggests that atmospheric temperature changes over Northern Europe and Greenland were coupled to SST variability and ice rafting. The records outline four major climatic phases: (i) an early-Holocene Thermal Maximum that lasted until approximately 6.7 kyr BP, (ii) a distinctly cooler phase associated with increased ice rafting between 6.5 and 3.7 kyr BP, (iii) a transition to generally warmer, but relatively unstable climate conditions between 3.7 and 2 kyr BP and (iv) a second distinct SST decline that took place between 2 and 0.5 kyr BP. In contrast to the dominant control of Northern Hemisphere summer insolation on early-Holocene climate development (via strong seasonality), the trigger for the onset of relatively unstable climatic conditions in the North Atlantic at 3.7 kyr BP is not straightforward. However, it is possible that this change was triggered by late-Holocene winter insolation increase at high northern latitude and/or by inter-hemispheric changes in orbital forcing. The late-Holocene Neoglaciation trend, which is characteristic of numerous terrestrial archives in northern Europe, may not only be attributed to a gradual decrease in orbitally forced summer temperature, but also to increase snow precipitation at high northern latitudes during generally milder winters. (C) 2004 Elsevier Ltd. All rights reserved.
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| 3. |
- Moros, M, et al.
(författare)
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Were glacial iceberg surges in the North Atlantic triggered by climatic warming?
- 2002
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Ingår i: Marine Geology. - 0025-3227. ; 192:4, s. 393-417
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Tidskriftsartikel (refereegranskat)abstract
- High-resolution physical, mineralogical, sedimentological and micropalaeontological studies were carried out on North Atlantic cores from the Reykjanes Ridge at 59degreesN and from the region southwest of the Faeroe Islands. All core sites are situated along the pathway of Iceland-Scotland Overflow Water (ISOW) and the various parameters measured display similar features. Previously identified carbonate oscillations [Keigwin and Jones (1994) J. Geophys. Res., 99, 12397-12410] in the time span back to the Marine Isotope Stage 5-4 transition and Late Glacial lithic events [Bond and Lotti (1995) Science, 267, 1005-1010], such as the Heinrich ice-rafting events, are all represented in the core records. Long-term trends and higher-frequency changes in ISOW intensity were reconstructed on the basis of various independent proxy records. The long-term trends in circulation match theoretical orbitally forced insolation changes. Our observed links between ice-rafted detritus (IRD) input, variations in sea surface temperature (SST) and circulation at greater depth point to the need to re-examine the origin of IRD events. We suggest that these events may have been triggered by enhanced, partly sub-surface, heat transport to the-north. Enhanced northward heat transport may have caused bottom melting of floating outlet glaciers and ice shelves, leading to increased iceberg discharge and ice sheet destabilization. This discharge. resulted in lower SST's and a lower temperature over Greenland. Thus, as shown by our records, this scenario implies a temporary de-coupling of surface processes and circulation at greater depth. A key feature is the occurrence of a-saw-tooth pattern in the marine data, which is similar to the Greenland ice core records. Moreover, the 'warming' theory of IRD events would explain the observed 'out-of-phase' relationship between the Greenland and Antarctic ice-core records and also the rapid establishment of higher temperatures over Greenland immediately after the cold phases (stadials) of the Dansgaard-Oeschger cycles.
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| 4. |
- Snowball, Ian, et al.
(författare)
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Saw-tooth pattern of North Atlantic current speed during Dansgaard-Oeschger cycles revealed by the magnetic grain size of Reykjanes Ridge sediments at 59 degrees N
- 2003
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Ingår i: Paleoceanography. - 0883-8305. ; 18:2
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Tidskriftsartikel (refereegranskat)abstract
- Detailed mineral (rock) magnetic measurements, including high-resolution magnetic hysteresis loops, were carried out on three sediment cores recovered from the Reykjanes Ridge in the North Atlantic. Supported by physical grain-size analyses, titanomagnetite grain-size variations form a proxy of the speed of near-bottom currents and reveal a cyclic ""saw-tooth'' pattern between Dansgaard-Oeschger cycles 8 and 5. The magnetic grain-size data suggest that these Dansgaard-Oeschger cycles were characterized by gradual intensification of the near-bottom current speed, while other paleoceanographic proxies indicate escalating iceberg discharge and declining sea surface temperatures. These observations are contrary to the frequently assumed and strictly applied positive relationship between high-latitude warmth and North Atlantic Deep Water formation. Within the confines of temporal control, however, it would appear that peaks in iceberg discharge and slow near-bottom current speeds were synchronous. The magnetic hysteresis data also demonstrate that magnetic concentration parameters, such as magnetic susceptibility, do not necessarily provide direct evidence of paleocirculation.
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| 5. |
- Tiljander, M, et al.
(författare)
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Documentation of the physical properties of annually laminated (varved) sediments at a sub-annual to decadal resolution for environmental interpretation
- 2002
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Ingår i: Quaternary International. - 1873-4553 .- 1040-6182. ; 88:1, s. 41406-41406
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Konferensbidrag (refereegranskat)abstract
- This paper describes a method to digitize high-resolution physical properties of annually laminated lake sediments. We modified a water-acetone epoxy exchange method in order to preserve all the fine structural details that varved sequences provide. By applying sediment microstratigraphical investigations (X-ray radiography, SEM) and semi-automatic image analysis, we were able to establish detailed information about varve composition and structure. Mineral magnetic measurements were also applied for comparison. By comparing all available physical data at high resolution, it will be possible to identify environmental changes that has occurred in the lake drainage basin.
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