1,390 research outputs found
Global change drives modern plankton communities away from the pre-industrial state
The ocean—the Earth’s largest ecosystem—is increasingly affected by anthropogenic climate change1,2. Large and globally consistent shifts have been detected in species phenology, range extension and community composition in marine ecosystems3,4,5. However, despite evidence for ongoing change, it remains unknown whether marine ecosystems have entered an Anthropocene6 state beyond the natural decadal to centennial variability. This is because most observational time series lack a long-term baseline, and the few time series that extend back into the pre-industrial era have limited spatial coverage7,8. Here we use the unique potential of the sedimentary record of planktonic foraminifera—ubiquitous marine zooplankton—to provide a global pre-industrial baseline for the composition of modern species communities. We use a global compilation of 3,774 seafloor-derived planktonic foraminifera communities of pre-industrial age9 and compare these with communities from sediment-trap time series that have sampled plankton flux since ad 1978 (33 sites, 87 observation years). We find that the Anthropocene assemblages differ from their pre-industrial counterparts in proportion to the historical change in temperature. We observe community changes towards warmer or cooler compositions that are consistent with historical changes in temperature in 85% of the cases. These observations not only confirm the existing evidence for changes in marine zooplankton communities in historical times, but also demonstrate that Anthropocene communities of a globally distributed zooplankton group systematically differ from their unperturbed pre-industrial state
Calcification depth of deep-dwelling planktonic foraminifera from the eastern North Atlantic constrained by stable oxygen isotope ratios of shells from stratified plankton tows
Stable oxygen isotopes (delta O-18) of planktonic foraminifera are one of the most used tools to reconstruct environmental conditions of the water column. Since different species live and calcify at different depths in the water column, the delta O-18 of sedimentary foraminifera reflects to a large degree the vertical habitat and interspecies delta O-18 differences and can thus potentially provide information on the vertical structure of the water column. However, to fully unlock the potential of foraminifera as recorders of past surface water properties, it is necessary to understand how and under what conditions the environmental signal is incorporated into the calcite shells of individual species. Deep-dwelling species play a particularly important role in this context since their calcification depth reaches below the surface mixed layer. Here we report delta O-18 measurements made on four deep-dwelling Globorotalia species collected with stratified plankton tows in the eastern North Atlantic. Size and crust effects on the delta O-18 signal were evaluated showing that a larger size increases the delta O-18 of G. inflata and G. hirsuta, and a crust effect is reflected in a higher delta O-18 signal in G. truncatulinoides. The great majority of the delta O-18 values can be explained without invoking disequilibrium calcification. When interpreted in this way the data imply depth-integrated calcification with progressive addition of calcite with depth to about 300m for G. inflata and to about 500m for G. hirsuta. In G. scitula, despite a strong subsurface maximum in abundance, the vertical delta O-18 profile is flat and appears dominated by a surface layer signal. In G. truncatulinoides, the delta O-18 profile follows equilibrium for each depth, implying a constant habitat during growth at each depth layer. The delta O-18 values are more consistent with the predictions of the Shackleton (1974) palaeotemperature equation, except in G. scitula which shows values more consistent with the Kim and O'Neil (1997) prediction. In all cases, we observe a difference between the level where most of the specimens were present and the depth where most of their shell appears to calcify.Agência financiadora Portuguese Foundation for Science and Technology (FCT): SFRH/BD/78016/2011;
UID/Multi/04326/2019
European Union Seventh Framework Programme (FP7/2007-2013): 228344-EUROFLEETS
German Research Foundation (DFG): WA2175/2-1; WA2175/4-1
German Climate Modelling consortium PalMod - German Federal Ministry of Education and Research (BMBF)info:eu-repo/semantics/publishedVersio
ForCenS, a curated database of planktonic foraminifera census counts in marine surface sediment samples
Census counts of marine microfossils in surface sediments represent an invaluable resource for paleoceanography and for the investigation of macroecological processes. A prerequisite for such applications is the provision of data syntheses for individual microfossil groups. Specific to such syntheses is the necessity of taxonomical harmonisation across the constituent datasets, coupled with dereplication of previous compilations. Both of these aspects require expert knowledge, but with increasing number of records involved in such syntheses, the application of expert knowledge via manual curation is not feasible. Here we present a synthesis of planktonic foraminifera census counts in surface sediment samples, which is taxonomically harmonised, dereplicated and treated for numerical and other inconsistencies. The data treatment is implemented as an objective and largely automated pipeline, allowing us to reduce the initial 6,984 records to 4,205 counts from unique sites and informative technical or true replicates. We provide the final product and document the procedure, which can be easily adopted for other microfossil data syntheses
Coccolithophore productivity at the western Iberian Margin during the Middle Pleistocene (310–455 ka) – evidence from coccolith Sr∕Ca data
Coccolithophores contribute significantly to marine
primary productivity and play a unique role in ocean biogeochemistry
by using carbon for photosynthesis (soft-tissue
pump) and for calcification (carbonate counter pump). Despite
the importance of including coccolithophores in Earth
system models to allow better predictions of the climate system’s
responses to planetary change, the reconstruction of
coccolithophore productivity mostly relied on proxies dependent
on accumulation and sedimentation rates and preservation
conditions. In this study we used an independent proxy,
based on the coccolith fraction (CF) Sr=Ca ratio, to reconstruct
coccolithophore productivity. We studied the marine
sediment core MD03-2699 from the western Iberian margin
(IbM), concentrating on glacial–interglacial cycles of Marine
Isotopic Stage (MIS) 12 to MIS 9. We found that IbM coccolithophore
productivity was controlled by changes in the
oceanographic conditions, such as in sea surface temperature
(SST) and nutrient availability, and by competition with
other phytoplankton groups. Long-term coccolithophore productivity
was primarily affected by variations in the dominant
surface water mass. Polar and subpolar surface waters
during glacial substages were associated with decreased
coccolithophore productivity, with the strongest productivity
minima concomitant with Heinrich-type events (HtEs). Subtropical, nutrient-poorer waters, increased terrigenous input,
and moderate to strong upwelling during the deglaciation
and early MIS11 are hypothesized to have attributed a
competitive advantage to diatoms to the detriment of coccolithophores,
resulting in intermediate coccolithophore productivity
levels. During the progression towards full glacial
conditions an increasing presence of nutrient-richer waters,
related to the growing influence of transitional surface waters
and/or intensified upwelling, probably stimulated coccolithophore
productivity to maxima following the rapid depletion
of silica by diatoms. We present conceptual models
of the carbon and carbonate cycle components for the IbM
in different time slices that might serve as a basis for further
investigation and modelling experiments.Fundação para a Ciência e a Tecnologia CCMAR (UID/Multi/04326/2019), (IF/01500/2014).info:eu-repo/semantics/publishedVersio
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