Sea-surface temperature reconstruction of sediments from the North Pacific and North Atlantic

Holocene climate variability is investigated in the North Pacific and North Atlantic realms, using alkenone-derived sea-surface temperature (SST) records as well as a millennial scale simulation with a coupled atmosphere-ocean general circulation model (AOGCM). The alkenone SST data indicate a temperature increase over almost the entire North Pacific from 7 cal kyr BP to the present. A dipole pattern with a continuous cooling in the northeastern Atlantic and a warming in the eastern Mediterranean Sea and the northern Red Sea is detected in the North Atlantic realm. Similarly, SST variations are opposite in sign between the northeastern Pacific and the northeastern Atlantic. A 2300 year long AOGCM climate simulation reveals a similar SST seesaw between the northeastern Pacific and the northeastern Atlantic on centennial time scales. Our analysis of the alkenone SST data and the model results suggests fundamental inter-oceanic teleconnections during the Holocene.

Biomarker distributions and calculated sea surface temperatures from the North Pacific Ocean

In order to study the modern sea surface characteristics of the sub-polar North Pacific and the Bering Sea, i.e. sea surface temperature (SST) and sea ice cover, surface sediments recovered during the RV Sonne Expedition 202 in 2009 were analysed. To distinguish between marine and terrestrial organic carbon, hydrogen index values, long chain n-alkanes and specific sterols have been determined. The results show that in the Bering Sea, especially on the sea slope, the organic carbon source is mainly caused by high primary production. In the North Pacific, on the other hand, the organic material originates predominantly from terrestrial higher plants, probably related to dust input from Asia. SST has been reconstructed using the modified alkenone unsaturation index. Calibration from Müller et al. (1998, doi:10.1016/S0016-7037(98)00097-0) offers the most reliable estimate of mean annual temperature in the central North Pacific but does not correlate with mean annual temperature throughout the study area. In the eastern North Pacific and the Bering Sea, the Sikes et al. (1997, doi:10.1016/S0016-7037(97)00017-3) calibration seems to be more accurate and matches summer SST. The distribution of the novel sea ice proxy IP25 (highly branched C25 isoprenoid alkene) in surface sediments is in accord with the modern spring sea ice edge and shows the potential of this proxy to track past variation in sea ice cover in the study area.

Stable carbon and oxygen isotope ratios of Late Miocene and Early Pliocene foraminifera from the Southwest Pacific

The Late Miocene-Early Pliocene paleoclimatic history has been evaluated for a deep drilled sediment sequence at Deep Sea Drilling Project Site 281 and a shallow water marine sediment sequence at Blind River, New Zealand, both of which lay within the Subantarctic water mass during the Late Miocene. A major, faunally determined, cooling event within the latest Miocene at Site 281 and Blind River coincides with oxygen isotopic changes in benthonic foraminiferal composition at DSDP Site 284 considered by Shackleton and Kennett (1975) to indicate a significant increase in Antarctic ice sheet volume. However, at Site 281 benthonic foraminiferal oxygen isotopic changes do not record such a large increase in Antarctic ice volume. It is possible that the critical interval is within an unsampled section (no recovery) in the latest Miocene. Two benthonic oxygen isotopic events in the Late Miocene (0.5 ? and 1 ? in the light direction) may be useful as time-stratigraphic markers. A permanent, negative, carbon isotopic shift at both Site 281 and Blind River allows precise correlations to be made between the two sections and to other sites in the Pacific region. Close interval sampling below the carbon shift at Site 281 revealed dramatic fluctuations in surface-water temperatures prior to a latest Miocene interval of refrigeration (Kapitean) and a strong pulse of dissolution between 6.6 and 6.2 +/- 0.1 m.y. which may be related to a fundamental geochemical change in the oceans at the time of the carbon shift (6.3-6.2 m.y.). No similar close interval sampling at Blind River was possible because of a lack of outcrop over the critical interval. Paleoclimatic histories from the two sections are very similar. Surface water temperatures and Antarctic ice-cap volume appear to have been relatively stable during the late Middle-early Late Miocene (early-late Tongaporutuan). By 6.4 m.y. cooler conditions prevailed at Site 281. Between 6.3 and 6.2 -+ 0.1 m.y. the carbon isotopic shift occurred followed, within 100,000 yr, by a distinct shallowing of water depths at Blind River. The earliest Pliocene (Opoitian) is marked by increasing surface-water temperatures.

Chemical composition of East Pacific Rise basal sediments

Analyses by atomic absorption spectrophotometry and spark-source mass spectrography of 25 basal metalliferous sediment units from widely spaced locations on the western flank of the East Pacific Rise show that the deposits are enriched relative to normal pelagic sediment in Fe, Mn, Ni, Cu, Pb, Zn, and many trace elements. The elements are partitioned differently between the various mineralogic constituents of the sediment, with Fe and Mn largely in separate phases and many of the remaining elements primarily associated with reducible ferromanganese oxide minerals but also with iron minerals and other phases. Most of the iron in the deposits is probably of volcanic origin, and much of the manganese and minor elements is derived from sea water. The bulk composition of the deposits varies with age; this is thought to be due to variations in the incidence of volcanic activity at the East Pacific Rise crest where the deposits were formed.

Element analyses and isotope composition of basalts from the West Valley segment, Juan de Fuca Ridge, northeast Pacific

The 50 km-long West Valley segment of the northern Juan de Fuca Ridge is a young, extension-dominated spreading centre, with volcanic activity concentrated in its southern half. A suite of basalts dredged from the West Valley floor, the adjacent Heck Seamount chain, and a small near-axis cone here named Southwest Seamount, includes a spectrum of geochemical compositions ranging from highly depleted normal (N-) MORB to enriched (E-) MORB. Heck Seamount lavas have chondrite-normalized La/Sm en -0.3, 87Sr/86Sr = 0.70235 - 0.70242, and 206Pb/204Pb = 18.22 - 18.44, requiring a source which is highly depleted in trace elements both at the time of melt generation and over geologic time. The E-MORB from Southwest Seamount have La/Sm en -1.8, 87Sr/86Sr = 0.70245 - 0.70260, and 206Pb/204Pb = 18.73 - 19.15, indicating a more enriched source. Basalts from the West Valley floor have chemical compositions intermediate between these two end-members. As a group, West Valley basalts from a two-component mixing array in element-element and element-isotope plots which is best explained by magma mixing. Evidence for crustal-level magma mixing in some basalts includes mineral-melt chemical and isotopic disequilibrium, but mixing of melts at depth (within the mantle) may also occur. The mantle beneath the northern Juan de Fuca Ridge is modelled as a plum-pudding, with "plums" of enriched, amphibole-bearing peridotite floating in a depleted matrix (DM). Low degrees of melting preferentially melt the "plums", initially removing only the amphibole component and producing alkaline to transitional E-MORB. Higher degrees of melting tap both the "plums" and the depleted matrix to yield N-MORB. The subtly different isotopic compositions of the E-MORBs compared to the N-MORBs require that any enriched component in the upper mantle was derived from a depleted source. If the enriched component crystallized from fluids with a DM source, the "plums" could evolve to their more evolved isotopic composition after a period of 1.5-2.0 Ga. Alternatively, the enriched component could have formed recently from fluids with a lessdepleted source than DM, such as subducted oceanic crust. A third possibility is that enriched material might be dispersed as "plums" throughout the upper mantle, transported from depth by mantle plumes.

Strontium-90 and tritium concentrations in surface waters of the North Pacific

Results of determinations of 90Sr and tritium polluting surface water in different parts of the North Pacific are presented. The T/90Sr ratio lies within 90-600 over the referred water area and attains 2000 near the Columbia River mouth. Tritium concentration in sea water has been noted to be affected by river runoff and terrigenous sediments.

Total biomass of mesoplankton and biomass of Calanus tonsus in the 0-200 m layer at stations in the Southwest Pacific

Structure of mesoplankton and distribution of dissolved ammonia in the vicinity of an isolated seamount of the Louisville Ridge in the subantarctic zone of the Pacific Ocean was studied using data obtained in January 1985 in an area 20 x 30 nm. There were areas with both high (20-25 to 139 g/m**2 in the 0-200 m layer) and low biomass values (<10 g/m**2) of mesoplankton. In the areas with high biomass, a single species Calanus tonsus was strongly dominant (>80% of biomass); its population was relatively mature in seasonal terms, with relatively high percentage of individuals containing fat inclusions. Stations with high mesoplankton biomass also had relatively high concentrations of dissolved ammonia. Presence of plankton-rich areas corre¬lated with presence of a quasi-steady-state topographic eddy. Lifetimes of these nonuniformities in the structure of mesoplankton are estimated as 10-30 days.