Stable oxygen isotope and Mg/Ca ratios of planktonic foraminifera from the Holocene and the Last Glacial Maximum

We measured oxygen isotopes and Mg/Ca ratios in the surface-dwelling planktonic foraminifer Globigerinoides ruber (white s.s.) and the thermocline dweller Pulleniatina obliquiloculata to investigate upper ocean spatial variability in the Indo-Pacific Warm Pool (IPWP). We focused on three critical time intervals: the Last Glacial Maximum (LGM; 18-21.5 ka), the early Holocene (8-9 ka), and the late Holocene (0-2 ka). Our records from 24 stations in the South China Sea, Timor Sea, Indonesian seas, and western Pacific indicate overall dry and cool conditions in the IPWP during the LGM with a low thermal gradient between surface and thermocline waters. During the early Holocene, sea surface temperatures increased by ~3°C over the entire region, indicating intensification of the IPWP. However, in the eastern Indian Ocean (Timor Sea), the thermocline gradually shoaled from the LGM to early Holocene, reflecting intensification of the subsurface Indonesian Throughflow (ITF). Increased surface salinity in the South China Sea during the Holocene appears related to northward displacement of the monsoonal rain belt over the Asian continent together with enhanced influx of saltier Pacific surface water through the Luzon Strait and freshwater export through the Java Sea. Opening of the freshwater portal through the Java Sea in the early Holocene led to a change in the vertical structure of the ITF from surface- to thermocline-dominated flow and to substantial freshening of Timor Sea thermocline waters.

(Table 1) Age, fork length, and tissue d15N and element concentration of arctic char (Salvelinus alpinus) from Lake Hazen

Arctic char (Salvelinus alpinus L.), the top predator in High Arctic lakes, often is used as a bioindicator of Hg contamination in Arctic aquatic ecosystems. The present study investigated effects of trophic position, size, and age of Arctic char in Lake Hazen, the largest lake in the Canadian High Arctic (81°50'N, 70°25'W), on Hg bioaccumulation. In addition, several essential (Se, K) and nonessential elements (Tl, Cs) in char muscle tissue were examined to compare their behavior to that of Hg. Trophic position of Arctic char was identified by stable isotope (d15N) signature. Temporal trends of Hg from seven sampling campaigns over a 16-year period (1990-2006) were investigated for the overall data and for one trophic class. Concentrations of Hg were not correlated with age but were positively related to fork length and trophic position. Large char with greater d15N signatures (>12 per mil) had larger Hg concentrations (0.09-1.63 µg/g wet wt) than small char with smaller d15N signatures (<12 per mil, 0.03-0.32 µg/g wet wt), indicating that Hg concentrations increased with trophic position. Nonessential Cs and Tl showed relationships to age, length, and trophic position similar to those of Hg, indicating their potential to bioaccumulate and biomagnify. Essential Se and K did not show these relationships. Concentrations of Hg were adjusted using d15N, leading to less within-year variability and a more consistent temporal trend. The d15N-adjusted trend showed no decline of Hg in Arctic char from Lake Hazen (1990-2006) in the overall data set and in the small morphotype. Trends for the same period before the adjustment were not significant for the overall data set, but a slight decrease was apparent in the small morphotype. The results confirm the need to consider trophic position and fish size when monitoring temporal trends of Hg, particularly for species with different morphotypes.

(Appendix) Analysis of benthic foraminifera from ODP Leg 181 and DSDP Leg 90

Canonical correspondence analysis indicates that the distribution of Neogene benthic foraminiferal faunas (>63 µm) in seven DSDP and ODP sites (500-4500 m water depth) east of New Zealand (38-51°S, 170°E-170°W) is most strongly influenced by depth (water mass stratification), and secondly by age (palaeoceanographic changes influencing faunal composition and biotic evolution). Stratigraphic faunal changes are interpretted in terms of the pulsed sequential development of southern, and later northern, polar glaciation and consequent cooling of bottom waters, increased vertical and lateral stratification of ocean water masses, and increased overall and seasonal surface water productivity. Oligocene initiation of the Antarctic Circumpolar Current and Deep Western Boundary Current (DWBC), flowing northwards past New Zealand, resulted in extensive hiatuses throughout the Southwest Pacific, some extending through into the Miocene. Planktic foraminiferal fragmentation index values indicate that carbonate dissolution was significant at abyssal depths throughout most of the Neogene, peaking at upper abyssal depths in the late Miocene (11-7 Ma), with the lysocline progressively deepened thereafter. Miocene abyssal faunas are dominated by Globocassidulina subglobosa and Oridorsalis umbonatus, with increasing Epistominella exigua after 16 Ma at upper abyssal depths. Peak abundances of Epistominella umbonifera indicate increased input of cold Southern Component Water to the DWBC at 7-6 Ma. Faunal association changes imply establishment of the modern Oxygen Minimum Zone (upper Circumpolar Deep Water) in the latest Miocene. Significant latitudinal differences between the benthic foraminiferal faunas at lower bathyal depths indicate the existence of an oceanic front along the Chatham Rise (location of present Subtropical Front), since the early late Miocene at least, with more pulsed productivity (higher E. exigua) along the south side. Modern Antarctic Intermediate Water faunal associations were established north of the Chatham Rise at 10-9 Ma, and south of it at 3-1.5 Ma. Middle-upper bathyal faunas on the Campbell Plateau are dominated by reticulate bolivinids during the early and middle Miocene, indicative of sustained productivity above relatively sluggish, suboxic bottom waters. Faunal changes and hiatuses indicate increased current vigour over the Campbell Plateau from the latest Miocene on. Surface water productivity (food supply) appears to have increased in three steps (at times of enhanced global cooling) marked by substantially increased relative abundance of: (1) Abditodentrix pseudothalmanni, Alabaminella weddellensis, Cassidulina norvangi (16-15 Ma, increased pulsed productivity); (2) Bulimina marginata f. aculeata, Nonionella auris, Trifarina angulosa, Uvigerina peregrina (3-1.5 Ma, increased overall productivity); and (3) Cassidulina carinata (1-0.5 Ma, increased overall productivity). Three intervals of deep-sea benthic foraminiferal taxonomic turnover are recognised (16-15, 11.5-10, 2-0.5 Ma) corresponding to intervals of enhanced global cooling and possible productivity changes. The late Pliocene-middle Pleistocene extinction, associated with increasing Northern Hemisphere glaciation, culminating in the middle Pleistocene climatic transition, was more significant in the study area than the earlier Neogene turnovers.

Photosynthetic parameters, chlorophyll concentration, and diffuse attenuation coefficients in the Rhode River, Maryland (USA), 1990-2009

Parameters in the photosynthesis-irradiance (P-E) relationship of phytoplankton were measured at weekly to bi-weekly intervals for 20 yr at 6 stations on the Rhode River, Maryland (USA). Variability in the light-saturated photosynthetic rate, PBmax, was partitioned into interannual, seasonal, and spatial components. The seasonal component of the variance was greatest, followed by interannual and then spatial. Physiological models of PBmax based on balanced growth or photoacclimation predicted the overall mean and most of the range, but not individual observations, and failed to capture important features of the seasonal and interannual variability. PBmax correlated most strongly with temperature and the concentration of dissolved inorganic carbon (IC), with lesser correlations with chlorophyll a, diffuse attenuation coefficient, and a principal component of the species composition. In statistical models, temperature and IC correlated best with the seasonal pattern, but temperature peaked in late July, out of phase with PBmax, which peaked in September, coincident with the maximum in monthly averaged IC concentration. In contrast with the seasonal pattern, temperature did not contribute to interannual variation, which instead was governed by IC and the additional lesser correlates. Spatial variation was relatively weak and uncorrelated with ancillary measurements. The results demonstrate that both the overall distribution of PBmax and its relationship with environmental correlates may vary from year to year. Coefficients in empirical statistical models became stable after including 7 to 10 yr of data. The main correlates of PBmax are amenable to automated monitoring, so that future estimates of primary production might be made without labor-intensive incubations.

(Table 2) Planktic foraminifera and their diversity indices of sediment surface samples from the Atlantic Ocean

Species distribution patterns in planktonic foraminiferal assemblages are fundamental to the understanding of the determinants of their ecology. Until now, data used to identify such distribution patterns was mainly acquired using the standard >150 µm sieve size. However, given that assemblage shell size-range in planktonic foraminifera is not constant, this data acquisition practice could introduce artefacts in the distributional data. Here, we investigated the link between assemblage shell size-range and diversity in Recent planktonic foraminifera by analysing multiple sieve-size fractions in 12 samples spanning all bioprovinces of the Atlantic Ocean. Using five diversity indices covering various aspects of community structure, we found that counts from the >63 µm fraction in polar oceans and the >125 µm elsewhere sufficiently approximate maximum diversity in all Recent assemblages. Diversity values based on counts from the >150 µm fraction significantly underestimate maximum diversity in the polar and surprisingly also in the tropical provinces. Although the new methodology changes the shape of the diversity/sea-surface temperature (SST) relationship, its strength appears unaffected. Our analysis reveals that increasing diversity in planktonic foraminiferal assemblages is coupled with a progressive addition of larger species that have distinct, offset shell-size distributions. Thus, the previously documented increase in overall assemblage shell size-range towards lower latitudes is linked to an expanding shell-size disparity between species from the same locality. This observation supports the idea that diversity and shell size-range disparity in foraminiferal assemblages are the result of niche separation. Increasing SST leads to enhanced surface water stratification and results in vertical niche separation, which permits ecological specialisation. Specific deviations from the overall diversity and shell-size disparity latitudinal pattern are seen in regions of surface-water instability, indicating that coupled shell-size and diversity measurements could be used to reconstruct water column structures of past oceans.

Element analyses and isotopic composition of basalts from the western Pacific

New Sr- Nd- and Pb-isotopic and trace element data are presented on basalts from the Sulu and Celebes Basins, and the submerged Cagayan Ridge Arc (Western Pacific), recently sampled during Ocean Drilling Program Leg 124. Drilling has shown that the Sulu Basin developed about 18 Ma ago as a backarc basin, associated with the now submerged Cagayan Ridge Arc, whereas the Celebes Basin was generated about 43 Ma ago, contemporaneous with a general plate reorganisation in the Western Pacifc, subsequently developing as an open ocean receiving pelagic sediments until the middle Miocene. In both basins, a late middle Miocene collision phase and the onset of volcanic activity on adjacent arcs in the late Miocene are recorded. Covariations between 87Sr/86Sr and 143Nd/144Nd show that the seafoor basalts from both the Sulu and Celebes Basins are isotopically similar to depleted Indian mid-ocean ridge basalts (MORB), and distinct from East Pacifc Rise MORB, defining a single negative correlation. The Cagayan Arc volcanics are different, in that they have distinctly lower epsilon-Ne(T) for a given epsilon-Sr(T), compared to Sulu and Celebes basalts. In the 207Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb diagrams, the Celebes, Sulu and Cagayan rocks all plot distinctly above the Northern Hemisphere Reference Line, with high Delta 7/4 Pb (5.3-9.3) and Delta 8/4 Pb (46.3-68.1) values. They define a single trend of radiogenic lead enrichment from Celebes through Sulu to Cagayan Ridge, within the Indian Ocean MORB data field. The data suggest that the overall chemical and isotopic features of the Sulu, Cagayan and Celebes rocks may be explained by partial melting of a depleted asthenospheric N-MORB-type ("normal") mantle source with isotopic characteristics similar to those of the Indian Ocean MORB source. This asthenospheric source was slightly heterogeneous, giving rise to the Sr-Nd isotopic differences between the Celebes and Sulu basalts, and the Cagayan Ridge volcanics. In addition, a probably slab-derived component enriched in LILE and LREE is required to generate the elemental characteristics and low Ne(T) of the Cagayan Ridge island arc tholeiitic and calcalkaline lavas, and to contribute to a small extent in the backarc basalts of the Sulu Sea. The results of this study confirm and extend the widespread Indian Ocean MORB signature in the Western Pacifc region. This signature could have been inherited by the Indian Ocean mantle itself during the rupture of Gondwanaland, when fragments of this mantle could have migrated towards the present position of the Celebes, Sulu and Cagayan sources.

Population and life-stage specific sensitivities to temperature and salinity stress in barnacles

Temperature and salinity shape the distribution and genetic structure of marine communities. Future warming and freshening will exert an additional stress to coastal marine systems. The extent to which organisms respond to these shifts will, however, be mediated by the tolerances of all life-stages and populations of species and their potential to adapt. We investigated nauplius and cypris larvae of the barnacle Balanus (Amphibalanus) improvisus from the Swedish west coast with respect to temperature (12, 20, and 28 °C) and salinity (5, 15, and 30) tolerances. Warming accelerated larval development and increased overall survival and subsequent settlement success. Nauplii developed and metamorphosed best at intermediate salinity. This was also observed in cypris larvae when the preceding nauplii stages had been reared at a salinity of 30. Direct comparisons of the present findings with those on a population from the more brackish Baltic Sea demonstrate contrasting patterns. We conclude that i) B. improvisus larvae within the Baltic region will be favoured by near-future seawater warming and freshening, that ii) salinity tolerances of larvae from the two different populations reflect salinities in their native habitats, but are nonetheless suboptimal and that iii) this species is generally highly plastic with regard to salinity.

Downwelling spectral irradiance as measured in different depths, remote sensing reflectance and phytoplankton pigment concentration during POLARSTERN cruises ANT-XXIV/1, ANT-XXIV/4, ANT-XXVI/4 and Maria S. Merian cruise MSM18/3

The composition and abundance of algal pigments provide information on phytoplankton community characteristics such as photoacclimation, overall biomass and taxonomic composition. In particular, pigments play a major role in photoprotection and in the light-driven part of photosynthesis. Most phytoplankton pigments can be measured by high-performance liquid chromatography (HPLC) techniques applied to filtered water samples. This method, as well as other laboratory analyses, is time consuming and therefore limits the number of samples that can be processed in a given time. In order to receive information on phytoplankton pigment composition with a higher temporal and spatial resolution, we have developed a method to assess pigment concentrations from continuous optical measurements. The method applies an empirical orthogonal function (EOF) analysis to remote-sensing reflectance data derived from ship-based hyperspectral underwater radiometry and from multispectral satellite data (using the Medium Resolution Imaging Spectrometer - MERIS - Polymer product developed by Steinmetz et al., 2011, doi:10.1364/OE.19.009783) measured in the Atlantic Ocean. Subsequently we developed multiple linear regression models with measured (collocated) pigment concentrations as the response variable and EOF loadings as predictor variables. The model results show that surface concentrations of a suite of pigments and pigment groups can be well predicted from the ship-based reflectance measurements, even when only a multispectral resolution is chosen (i.e., eight bands, similar to those used by MERIS). Based on the MERIS reflectance data, concentrations of total and monovinyl chlorophyll a and the groups of photoprotective and photosynthetic carotenoids can be predicted with high quality. As a demonstration of the utility of the approach, the fitted model based on satellite reflectance data as input was applied to 1 month of MERIS Polymer data to predict the concentration of those pigment groups for the whole eastern tropical Atlantic area. Bootstrapping explorations of cross-validation error indicate that the method can produce reliable predictions with relatively small data sets (e.g., < 50 collocated values of reflectance and pigment concentration). The method allows for the derivation of time series from continuous reflectance data of various pigment groups at various regions, which can be used to study variability and change of phytoplankton composition and photophysiology.

(Fig. 1D, 3E) Sea surface temperature and alkenone C37:4 for sediment core MD01-2444 during the penultimate glaciation

Past glacials can be thought of as natural experiments in which variations in boundary conditions influenced the character of climate change. However, beyond the last glacial, an integrated view of orbital- and millennial-scale changes and their relation to the record of glaciation has been lacking. Here, we present a detailed record of variations in the land-ocean system from the Portuguese margin during the penultimate glacial and place it within the framework of ice-volume changes, with particular reference to European ice-sheet dynamics. The interaction of orbital- and millennial-scale variability divides the glacial into an early part with warmer and wetter overall conditions and prominent climate oscillations, a transitional mid-part, and a late part with more subdued changes as the system entered a maximum glacial state. The most extreme event occurred in the mid-part and was associated with melting of the extensive European ice sheet and maximum discharge from the Fleuve Manche river. This led to disruption of the meridional overturning circulation, but not a major activation of the bipolar seesaw. In addition to stadial duration, magnitude of freshwater forcing, and background climate, the evidence also points to the influence of the location of freshwater discharges on the extent of interhemispheric heat transport.