Ice rafted debris, tetra-unsaturated alkenone and reconstructed sea surface temperature in sediment of ODP Hole 104-642B

Abstract of paper will be inserted here...

Planktic foraminiferal distribution and stable isotope ratios of sediment core MSM05/5_712-1 from the Arctic Ocean

The Arctic is responding more rapidly to global warming than most other areas on our planet. Northward flowing Atlantic Water is the major means of heat advection towards the Arctic and strongly affects the sea ice distribution. Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only ~150 years. Here, we present a multidecadal scale record of ocean temperature variations during the last 2000 years, derived from marine sediments off Western Svalbard (79°N). We find that early-21st-century temperatures of Atlantic Water entering the Arctic Ocean are unprecedented over the past 2000 years and are presumably linked to the Arctic Amplification of global warming.

Mediterranean cold-water coral measurements

This study presents aggradation rates supplemented for the first time by carbonate accumulation rates from Mediterranean cold-water coral sites considering three different regional and geomorphological settings: (i) a cold-water coral ridge (eastern Melilla coral province, Alboran Sea), (ii) a cold-water coral rubble talus deposit at the base of a submarine cliff (Urania Bank, Strait of Sicily) and (iii) a cold-water coral deposit rooted on a predefined topographic high overgrown by cold-water corals (Santa Maria di Leuca coral province, Ionian Sea). The mean aggradation rates of the respective cold-water coral deposits vary between 10 and 530 cm kyr?1 and the mean carbonate accumulation rates range between 8 and 396 g cm?2 kyr?1 with a maximum of 503 g cm?2 kyr?1 reached in the eastern Melilla coral province. Compared to other deep-water depositional environments the Mediterranean cold-water coral sites reveal significantly higher carbonate accumulation rates that were even in the range of the highest productive shallow-water Mediterranean carbonate factories (e.g. Cladocora caespitosa coral reefs). Focusing exclusively on cold-water coral occurrences, the carbonate accumulation rates of the Mediterranean cold-water coral sites are in the lower range of those obtained for the prolific Norwegian coral occurrences, but exhibit much higher rates than the cold-water coral mounds off Ireland. This study clearly indicates that cold-water corals have the potential to act as important carbonate factories and regional carbonate sinks within the Mediterranean Sea. Moreover, the data highlight the potential of cold-water corals to store carbonate with rates in the range of tropical shallow-water reefs. In order to evaluate the contribution of the cold-water coral carbonate factory to the regional or global carbonate/carbon cycle, an improved understanding of the temporal and spatial variability in aggradation and carbonate accumulation rates and areal estimates of the respective regions is needed.

Opal concentration of ODP Leg 178 holes

Neogene to Quaternary records of biogenic opal contents and opal accumulation rates are presented for Sites 1095, 1096, and 1101, which were drilled during Ocean Drilling Program Leg 178 in the Bellingshausen Sea, a marginal sea in the eastern Pacific sector of the Southern Ocean. The opal records in the drift sediments on the continental rise west of the Antarctic Peninsula provide signals of paleoproductivity, although they are influenced by dissolution in the water column and the sediment column. Opal contents at Sites 1095, 1096, and 1101 show similar long-term trends through the Neogene and Quaternary, whereas the opal accumulation rates exhibit marked discrepancies, which are caused by local differences in opal preservation linked to local variations of bottom current-induced supply of lithogenic detritus. We used a regression describing the relationship between opal preservation and sedimentation rate to extract the signal of primary opal deposition on the seafloor in the Bellingshausen Sea from the opal accumulation in the drift deposits. On long-term timescales, the reconstructed opal depositional rates show patterns similar to those of the opal contents and a much better coherency between the different locations on the Antarctic Peninsula continental rise. Therefore, the estimated opal depositional rates are suggested to represent a suitable proxy for paleoproductivity in the drift setting of the Bellingshausen Sea. Supposing that the sea-ice coverage within the Antarctic Zone was the main factor controlling biological productivity in the Bellingshausen Sea, and thus the estimated opal depositional rates on the continental rise, we reconstructed paleoceanographic long-term changes during the Neogene and Quaternary considering the climatic control on regional and global scales. Slightly enhanced opal depositional rates during the late Miocene are interpreted to indicate warmer climatic conditions in the vicinity of the Antarctic Peninsula than at present. The contribution of heat from the Northern Component Water (NCW) into the Southern Ocean seems only to have played a subordinate role during that time. High opal depositional rates during the early Pliocene document a strong reduction of sea-ice coverage and relatively warm climatic conditions in the Bellingshausen Sea. The early onset of the Pliocene warmth points to a positive feedback of regional Antarctic climate on the global thermohaline circulation. A decrease of opal deposition between 3.1 and 1.8 Ma likely reflects sea-ice expansion in response to reduced NCW flow, caused by the onset and intensification of Northern Hemisphere glaciation. Throughout the Quaternary, a relatively constant level of opal depositional rates in the Bellingshausen Sea indicates stable climatic conditions in the Antarctic Peninsula area.

Stable isotopes, CaCO3, opal and terrigeneous of ODP Site 108-663 (Table A1)

High- and low-latitude forcing of terrestrial African paleoclimate variability is demonstrated using 900 ka eolian and biogenic component records from Ocean Drilling Program site 663 in the eastern equatorial Atlantic. Terrigenous (eolian dust) and phytolith (savannah grass cuticle) accumulation rate records vary predominantly at 100 and 41 kyr periodicities and spectral phase estimates implicate high-latitude forcing. The abundance of freshwater diatoms (Melosira) transported from dry African lake beds varies coherently at 23-19 kyr orbital periodicities and at a phasing which implicates low-latitude precessional monsoon forcing. Modeling studies demonstrate that African climate is sensitive to both high- and low-latitude boundary conditions. African monsoon intensity is modulated by direct insolation variations due to orbital precession, whereas remote high-latitude forcing can be related to cool North Atlantic sea surface temperatures (SSTs) which promote African aridity and enhance dust-transporting wind speeds. The site 663 terrigenous and phytolith records covary with North Atlantic SST variability at 41 °N (site 607). We suggest that Pleistocene African climate has responded to both high-latitude North Atlantic SST variability as well as low-latitude precessional monsoon forcing; the high-latitude influence dominates the sedimentary record. Prior to circa 2.4 Ma, terrigenous variations occurred primarily at precessional periodicities (23-19 kyr), indicating that African climate was largely controlled by low-latitude insolation variations prior to the onset of high-amplitude glacial-interglacial climate change.

Biogenic opal in Late Pleistocene sediments of ODP Leg 177 holes

Sediments in the southeast Atlantic sector of the Southern Ocean were cored during Ocean Drilling Program (ODP) Leg 177 to study the paleoceanographic history of the Antarctic region on short (millennial) to long (Cenozoic) timescales. Seven sites were drilled along a north-south transect across the Antarctic Circumpolar Current (ACC) from 41° to 53°S. The general goals of Leg 177 were twofold: (1) to document the biostratigraphic, biogeographic, and paleoceanographic history of the Paleogene and early Neogene, a period marked by the establishment of the Antarctic cryosphere and the ACC, and (2) to target expanded sections of late Neogene sediments, which can be used to resolve the timing of Southern Hemisphere climatic events on orbital and suborbital time scales (Gersonde, Hodell, Blum, et al., 1999, doi:10.2973/odp.proc.ir.177.1999). Closely spaced measurements of sedimentary physical properties were obtained from all cores recovered during Leg 177 using the ODP whole-round multisensor track. In addition, high-resolution diffuse color reflectance and resistivity measurements were collected on the Oregon State University Split Core Analysis Track. These whole-core and split-core measurements provide high-resolution proxy data sets for the estimation of biogenic and terrigenous mineralogy and mass flux. To assist investigators in calibrating these proxy data sets from sites located within the circum-Antarctic opal belt, samples from Sites 1093 (50°S) and 1094 (53°S) were analyzed for biogenic opal content.

Biogenic opal and carbonate concentration in late Neogene sediments of ODP Site 114-704

A preliminary composite depth section was generated for Site 704 by splicing Holes 704A and 704B together over the interval 0-350 mbsf (0-9 m.y.). High-resolution carbonate and opal data from the cores were correlated with the calcium and silicon signals from the GST logging run in Hole 704B to identify missing and disturbed intervals in the cores. Paleomagnetic and biostratigraphic age boundaries were then transferred to the composite depth records to obtain an age model, and sedimentation rates were calculated by linear interpolation between datums. Algorithms relating measured dry-bulk density to carbonate content and depth were generated to produce predicted values of density for every sample. Accumulation rates of bulk, carbonate, opal, and terrigenous sediment components were then computed to generate a record of sediment deposition on the Meteor Rise that has a resolution of better than 200,000 yr for the period from 8.6 to 1.0 m.y. From 8.6 to 2.5 m.y., bulk-accumulation rates on the Meteor Rise averaged less than 2 g/cm**2/1000 yr and were dominated by carbonate deposition. The first significant opal deposition (6.0 m.y.) punctuated a brief (less than 0.6 Ma) approach of the Polar Front Zone (PFZ) northward that heralded a period of increasing severity of periodic carbonate dissolution events (terrigenous maxima) that abruptly terminated at 4.8 m.y. (base of the Thvera Subchron), synchronous with the reflooding of the Mediterranean after the Messinian salinity crisis. From 4.8 to 2.5 m.y., carbonate again dominated deposition, and the PFZ was far south except during brief northward excursions bracketing 4.2-3.9, 3.3-2.9, and 2.8-2.7 m.y. At 2.5 m.y., all components of bulk-accumulation rates increased dramatically (up to 15 g/cm2/1000 yr), and by 2.4 m.y., a pattern of alternating, high-amplitude carbonate and opal cyclicity marked the initiation of rapid glacial to interglaci·l swings in the position of the PFZ, synchronous with the "onset" of major Northern Hemisphere glaciation. Both mass-accumulation rates and the amplitude of the cycles decreased by about 2 m.y., but opal accumulation rates remained high up through the base of the Jaramillo (0.98 m.y.). From 1.9 to 1 m.y., the record is characterized by moderate amplitude fluctuations in carbonate and opal. This record of opal accumulation rates is interpreted as a long-term "Polar Front Indicator" that monitors the advance and retreat of the opal-rich PFZ northward (southward) toward (away from) the Meteor Rise in the subantarctic sector of the South Atlantic Ocean. The timing of PFZ migrations in the subantarctic South Atlantic Ocean is remarkably similar to Pliocene-Pleistocene climate records deduced from benthic oxygen isotope records in the North Atlantic Ocean (Raymo et al., 1989, doi:10.1029/PA004i004p00413; Ruddiman et al., 1989, doi:10.1029/PA004i004p00353). These include northward migrations during "cold" intervals containing strong glacial isotope stages (2.4-2.3, 2.1-2.0, 1.95-1.55, 1.45-1.30 m.y. and at about 1.13 and 1.09 m.y.) and southward migrations during "warm" intervals containing weak glacial and/or strong interglacial stages (2.45-2.40, 2.30-2.10, 2.00-1.95, 1.52-1.45, 1.30-1.18, 1.11, and 1.06-0.93 m.y.). Although our preliminary composite record is not continuous (some stages are obviously missing), there is hope that future work will identify these missing intervals in the as yet incomplete Hole 704B and will extend this high-resolution Southern Hemisphere climate record back to 8.6 m.y.