Hydrographic conditions along the western Iberian margin during marine isotope stage 2

The surface water hydrography along the western Iberian margin, as part of the North Atlantic's eastern boundary upwelling system, consists of a complex, seasonally variable system of equatorward and poleward surface and subsurface currents and seasonal upwelling. Not much information exists to ascertain if the modern current and productivity patterns subsisted under glacial climate conditions, such as during marine isotope stage (MIS) 2, and how North Atlantic meltwater events, especially Heinrich events, affected them. To help answer these questions we are combining stable isotope records of surface to subsurface dwelling planktonic foraminifer species with sea surface temperature and export productivity data for four cores distributed along the western and southwestern Iberian margin (MD95-2040, MD95-2041, MD99-2336, and MD99-2339). The records reveals that with the exception of the Heinrich events and Greenland Stadial (GS) 4 hydrographic conditions along the western Iberian margin were not much different from the present. During the Last Glacial Maximum (LGM), subtropical surface and subsurface waters penetrated poleward to at least 40.6°N (site MD95-2040). Export productivity was, in general, high on the western margin during the LGM and low in the central Gulf of Cadiz, in agreement with the modern situation. During the Heinrich events and GS 4, on the other hand, productivity was high in the Gulf of Cadiz and suppressed in the upwelling regions along the western margin where a strong halocline inhibited upwelling. Heinrich event 1 had the strongest impact on the hydrography and productivity off Iberia and was the only period when subarctic surface waters were recorded in the central Gulf of Cadiz. South of Lisbon (39°N), the impact of the other Heinrich events was diminished, and not all of them led to a significant cooling in the surface waters. Thus, climatic impacts of Heinrich events highly varied with latitude and the prevailing hydrographic conditions in this region

Late Quaternary calcium carbonate sedimentation and terrigenous input along the east Greenland continental margin

Nine large box cores collected in the western Greenland-Iceland-Norwegian (GIN) Sea were analyzed for calcium carbonate content and coarse fraction components. Stratigraphic control is based on oxygen isotope records performed on four of the cores. All cores were correlated using oxygen and carbon isotope data, fluctuations in calcium carbonate content, coarse terrigenous particle content and volcanic ash beds. Glacial and interglacial cycles are documented by a number of terrigenous particle events and differentiated calcium carbonate production which can be correlated to major paleoceanographic and paleoclimatic shifts. In the older core sections, extensive deposition of ice-rafted detritus (IRD) persisted until about oxygen isotope stage 9 and document a relatively stable environment in this area, strongly influenced by cold surface water masses. The following interval was characterized by variations in the general surface water circulation pattern, although high amounts of IRD are still present in Iceland Sea sediments. Pronounced shifts in terrigenous input and pelagic carbonate records were identified close to the oxygen isotope stage Full-size image (<1 K) and Full-size image (<1 K) boundaries, indicating massive melting of icebergs in the western GIN Sea. These enormous inputs of debris were followed by an increase in calcium carbonate production caused by maximum intrusion of warm Atlantic surface waters. Relatively high calcium carbonate contents also show that only little dilution by fine-grained material and a minimum of ice melting occurred during these warm phases. During oxygen isotope stage 5, conditions were more uniform indicating a less pronounced westward penetration of Atlantic waters as compared to the Holocene. The last glacial (stages 4-2) is characterized by the occurrence of “Heinrich”-like events, although high IRD contents were present throughout this interval. A distinct contrast between the northernmost cores and the cores in the south is indicative of a rather strong westward penetration of Atlantic water in the north and of an area dominated by cold water east of the Kolbeinsey Ridge during the Holocene. However, conditions west of Jan Mayen seem to have remained constantly dominated by cold surface waters throughout the whole time investigated

Eastern Mediterranean surface water temperatures and d18O composition during deposition of sapropels in the late Quaternary

Water column stratification increased at climatic transitions from cold to warm periods during the lateQuaternary and led to anoxic conditions and sapropel formation in the deep eastern Mediterranean basins. Highresolutiondata sets on sea-surface temperatures (SST) (estimated from U37k0 indices) and d18O of planktonicforaminifer calcite (d18Ofc) across late Pleistocene sapropel intervals show that d18Ofc decreased (between 1 and4.6%) and SST increased (between 0.7 and 6.7 C). Maximal d18Oseawater depletion of eastern Mediterraneansurface waters at the transition is between 0.5 and 3.0%, and in all but one case exceeded the depletion seen in awestern Mediterranean core. The depletion in d18Oseawater is most pronounced at sapropel bases, in agreementwith an initial sudden input of monsoon-derived freshwater. Most sapropels coincide with warming trends ofSST. The density decrease by initial freshwater input and continued warming of the sea surface pooled freshwater in the surface layer and prohibited deep convection down to ageing deep water emplaced during cold andarid glacial conditions. An exception to this pattern is glacial sapropel S6; its largest d18Oseawater depletion(3%) is almost matched by the depletion in the western Mediterranean Sea, and it is accompanied by surfacewater cooling following an initially rapid warming phase. A second period of significant isotopic depletion is inisotope stage 6 at the 150 kyr insolation maximum. While not expressed as a sapropel due to cold SST, it is inaccord with a strengthened monsoon in the southern catchment

A high-quality annually laminated sequence from Lake Belau, Northern Germany: Revised chronology and its implications for palynological and tephrochronological studies

The annually laminated record of Lake Belau offers an exceptional opportunity to investigate with high temporal resolution Holocene environmental change, aspects of climate history and human impact on the landscape. A new chronology based on varve counts, 14C-datings and heavy metal history has been established, covering the last 9400 years. Based on multiple varve counting on two core sequences, the easily countable laminated section spans about 7850 varve years (modelled age range c. 9430 to 1630 cal. BP). Not all of the record is of the same quality but approximately 69% of the varves sequence is classified to be of high quality and only c. 5% of low quality. The new chronology suggests dates generally c. 260 years older than previously assumed for the laminated section of the record. The implications for the vegetation and land-use history of the region as well as revised datings for pollen stratigraphical events are discussed. Tephra analysis allowed the identification of several cryptotephra layers. New dates for volcanic eruptions are presented for the Lairg B event (c. 6848 cal. BP, 2s range 6930–6713 cal. BP), the Hekla 4 event (c. 4396 cal. BP, 2s range 4417–4266 cal. BP), and Hekla 3 eruption (c. 3095 cal. BP, 2s range 3120–3068 cal. BP)

Potential links between surging ice sheets, circulation changes and the Dansgaard Oeschger cycles in the Irminger Sea, 60-18 kyr.

Surface and deepwater paleoclimate records in Irminger Sea core SO82-5 (59°N, 31°W) and Icelandic Sea core PS2644 (68°N, 22°W) exhibit large fluctuations in thermohaline circulation (THC) from 60 to 18 calendar kyr B.P., with a dominant periodicity of 1460 years from 46 to 22 calendar kyr B.P., matching the Dansgaard-Oeschger (D-O) cycles in the Greenland Ice Sheet Project 2 (GISP2) temperature record [Grootes and Stuiver, 1997]. During interstadials, summer sea surface temperatures (SST<inf>su</inf>) in the Irminger Sea averaged to 8°C, and sea surface salinities (SSS) averaged to ∼36.5, recording a strong Irminger Current and Atlantic THC. During stadials, SST<inf>su</inf> dropped to 2°-4°C, in phase with SSS drops by ∼1-2. They reveal major meltwater injections along with the East Greenland Current, which turned off the North Atlantic deepwater convection and hence the heat advection to the north, in harmony with various ocean circulation and ice models. On the basis of the IRD composition, icebergs came from Iceland, east Greenland, and perhaps Svalbard and other northern ice sheets. However, the southward drifting icebergs were initially jammed in the Denmark Strait, reaching the Irminger Sea only with a lag of 155-195 years. We also conclude that the abrupt stadial terminations, the D-O warming events, were tied to iceberg melt via abundant seasonal sea ice and brine water formation in the meltwater-covered northwestern North Atlantic. In the 1/1460-year frequency band, benthic δ18O brine water spikes led the temperature maxima above Greenland and in the Irminger Sea by as little as 95 years. Thus abundant brine formation, which was induced by seasonal freezing of large parts of the northwestern Atlantic, may have finally entrained a current of warm surface water from the subtropics and thereby triggered the sudden reactivation of the THC. In summary, the internal dynamics of the east Greenland ice sheet may have formed the ultimate pacemaker of D-O cycles

Experimental Determination of the Ontogenetic Stable Isotope Variability in two Morphotypes of Globigerinella siphonifera (d'Orbigny).

Carbon and oxygen isotope fractionation in two morphotypes (Type I and Type II) of the symbiont bearing planktic foraminifer Globigerinella siphonifera (d'Orbigny) is investigated. SCUBA collected specimens were grown in the laboratory under identical culture conditions and their stable isotope signature was analyzed to characterize the influence of ontogeny and feeding rate on their d13C and d18O signals. The two Types show a positive linear correlation between d13C and d18O with size. Type II is enriched in 13C and 18O relative to Type I and the enrichment per size increment is greater than for Type I. The carbon isotope composition of Type I tends towards lighter values at higher feeding rates whereas Type II is unaffected by the feeding regime.In order to determine if the isotopic response can be attributed to differences in growth characteristics and/or host/symbiont interactions, specimens were cultured under a variety of conditions and the pigment composition of freshly collected specimens was measured. Type I has a much lower photo-pigment content, which probably implies a lower gross photosynthetic rate. In addition, its growth- and calcification- rate are lower. The impact of these life processes on the stable isotope composition is discussed and it is argued that isotope fractionation is controlled by two linked processes. The carbon isotope fractionation is affected directly by a 12C depletion or enrichment of the microenvironment via symbiont photosynthesis and host respiration respectively. Concurrently, the life processes invoke a kinetic fractionation of the carbon and oxygen isotopes via their impact on the ambient carbonate chemistry