Organic temperature proxies in the subpolat region around Iceland

Subpolar regions are key areas to study natural climate variability, due to their high sensitivity to rapid environmental changes, particularly through sea surface temperature (SST) variations. Here, we have tested three independent organic temperature proxies (UK'37, TEX86 and LDI) on their potential applicability for SST reconstruction in the subpolar region around Iceland. UK'37, TEX86 and TEXL86 temperature estimates from suspended particulate matter showed a substantial discrepancy with instrumental data, while long chain alkyl diols were below detection limit in most of the stations. In the northern Iceland Basin, sedimenting particles revealed a seasonality in lipid fluxes i.e. high fluxes of alkenones and GDGTs were measured during late spring-summer, and high fluxes of long chain alkyl diols during late summer. The flux-weighted average temperature estimates had a significant negative (ca. 2.3°C for UK'37) and positive (up to 5°C for TEX86) offset with satellite-derived SSTs and temperature estimates derived from the underlying surface sediment. UK'37 temperature estimates from surface sediments around Iceland correlate well with summer mean sea surface temperatures, while TEX86 derived temperatures correspond with both annual and winter mean 0-200 m temperatures, suggesting a subsurface temperature signal. Anomalous LDI-SST values in surface sediments, and low mass flux of 1,13- and 1,15-diols compared to 1,14-diols, suggest that Proboscia diatoms are the major sources of long chain alkyl diols in this area rather than eustigmatophyte algae, and therefore the LDI cannot be applied in this region.

Diatom biostratigraphy and datum levels of sediments from ODP Leg 167 sites

Ocean Drilling Program Leg 167 represents the first time since 1978 that the North American Pacific margin was drilled to study ocean history. More than 7500 m of Quaternary to middle Miocene (14 Ma) sediments were recovered from 13 sites, representing the most complete stratigraphic sequence on the California margin. Diatoms are found in most samples in variable abundance and in a moderately well-preserved state throughout the sequence, and they are often dominated by robust, dissolution-resistant species. The Neogene North Pacific diatom zonation of Yanagisawa and Akiba (1998, doi:10.5575/geosoc.104.395) best divides the Miocene to Quaternary sequences, and updated ages of diatom biohorizons estimated based on the geomagnetic polarity time scale of Cande and Kent (1995, doi:10.1029/94JB03098) are slightly revised to adjust the differences between the other zonations. Most of the early middle Miocene through Pleistocene diatom datum levels that have been proven to be of stratigraphic utility in the North Pacific appear to be nearly isochronous within the level of resolution constrained by sample spacing. The assemblages are characterized by species typical of middle-to-high latitudes and regions of high surface-water productivity, predominantly by Coscinodiscus marginatus, Stephanopyxis species, Proboscia barboi, and Thalassiothrix longissima. Latest Miocene through Pliocene assemblages in the region of the California Current, however, are intermediate between those of subarctic and subtropical areas. As a result, neither the existing tropical nor the subarctic (high latitude) zonal schemes were applicable for this region. An interval of pronounced diatom dissolution detected throughout the Pliocene sequence apparently correspond to a relatively warmer paleoceanographic condition resulting in a slackening of the southward flow of the California Current.

Geochemistry and stratigraphy on sediment cores from Leg198 and Leg 208

The first complete cyclic sedimentary successions for the early Paleogene from drilling multiple holes have been retrieved during two ODP expeditions: Leg 198 (Shatsky Rise, NW Pacific Ocean) and Leg 208 (Walvis Ridge, SE Atlantic Ocean). These new records allow us to construct a comprehensive astronomically calibrated stratigraphic framework with an unprecedented accuracy for both the Atlantic and the Pacific Oceans covering the entire Paleocene epoch based on the identification of the stable long-eccentricity cycle (405-kyr). High resolution X-ray fluorescence (XRF) core scanner and non-destructive core logging data from Sites 1209 through1211 (Leg 198) and Sites 1262, 1267 (Leg 208) are the basis for such a robust chronostratigraphy. Former investigated marine (ODP Sites 1001 and 1051) and land-based (e.g., Zumaia) sections have been integrated as well. The high-fidelity chronology is the prerequisite for deciphering mechanisms in relation to prominent transient climatic events as well as completely new insights into Greenhouse climate variability in the early Paleogene. We demonstrate that the Paleocene epoch covers 24 long eccentricity cycles. We also show that no definite absolute age datums for the K/Pg boundary or the Paleocene - Eocene Thermal Maximum (PETM) can be provided by now, because of still existing uncertainties in orbital solutions and radiometric dating. However, we provide two options for tuning of the Paleocene which are only offset by 405-kyr. Our orbitally calibrated integrated Leg 208 magnetostratigraphy is used to revise the Geomagnetic Polarity Time Scale (GPTS) for Chron C29 to C25. We established a high-resolution calcareous nannofossil biostratigraphy for the South Atlantic which allows a much more detailed relative scaling of stages with biozones. The re-evaluation of the South Atlantic spreading rate model features higher frequent oscillations in spreading rates for magnetochron C28r, C27n, and C26n.

Planktonic foraminifera fluxes and stable isotope ratios in the Irminger Sea

Past water column stratification can be assessed through comparison of the d18O of different planktonic foraminiferal species. The underlying assumption is that different species form their shells simultaneously, but at different depths in the water column. We evaluate this assumption using a sediment trap time-series of Neogloboquadrina pachyderma (s) and Globigerina bulloides from the NW North Atlantic. We determined fluxes, d18O and d13C of shells from two size fractions to assess size-related effects on shell chemistry and to better constrain the underlying causes of isotopic differences between foraminifera in deep-sea sediments. Our data indicate that in the subpolar North Atlantic differences in the seasonality of the shell flux, and not in depth habitat or test size, determine the interspecies Delta d18O. N. pachyderma (s) preferentially forms from early spring to late summer, whereas the flux ofG. bulloides peaks later in the season and is sustained until autumn. Likewise, seasonality influences large and small specimens differently, with large shells settling earlier in the season. The similarity of the seasonal d18O patterns between the two species indicates that they calcify in an overlapping depth zone close to the surface. However, their d13C patterns are markedly different (>1 per mil). Both species have a seasonally variable offset from d13CDIC that appears to be governed primarily by temperature, with larger offsets associated with higher temperatures. The variable offset from d13CDIC implies that seasonality of the flux affects the fossil d13C signal, which has implications for reconstruction of the past oceanic carbon cycle.