The subpolar NE Atlantic Ocean experiences seasonal fluxes of labile organic matter (phytodetritus) which are expected to strongly influence the composition of benthic foraminiferal assemblages and ...benthic foraminiferal accumulation rates. We studied export production over the last 12 kyr at a sampling resolution of approximately 250–300 years through an investigation of bathyal benthic foraminiferal assemblages (>63 μm) at Ocean Drilling Program (ODP) Site 980 on the Feni Drift (55°29′N, 14°42′W, 2179 m water depth).
During the last 12 kyr, faunas at Site 980 were dominated (~75%) by Cassidulina obtusa, Nonionella iridea, Bolivina difformis, Trifarina pauperata, Alabaminella weddellensis, Stainforthia fusiformis, Cassidulina laevigata and Eilohedra vitrea. The absolute and relative abundances and diversity of these and other species varied significantly. In the interval ~12–10 ka, A. weddellensis, S. fusiformis and T. pauperata had higher % abundance (named here ‘H10 species’), but this is not reflected in a higher accumulation rate, suggesting that surface productivity was low, at highly variable conditions. Species at lower % abundance during this time include B. difformis, C. laevigata, C. obtusa, E. vitrea and N. iridea (so-called ‘L10 species’). The ‘8.2 ka cold event’ was characterized by increased carbonate dissolution (reflected in decreases in the absolute abundance, benthic foraminifera accumulation rate, weight % coarse fraction, and presence of poorly preserved/fragmented benthic foraminifera). Peaks in the relative abundance of species which, in our opinion, exploited phytodetritus (‘phytodetritus species’: N. iridea, A. weddellensis, C. obtusa, and rare Epistominella exigua) occurred at 8.0 ka, 7.0 ka, 6.3–5.6 ka, 4.7 ka, 4.3–3.4 ka and 2.4 ka. These peaks generally correspond to peaks in absolute abundance (number of specimens per gram, accumulation rate), indicating increases in the seasonality of export productivity. However, the ‘phytodetritus species’ do not covary in absolute and relative abundance over the studied interval, suggesting that they have somewhat different ecological requirements.
There appears to be no simple relationship between changes in the degree of seasonality of export productivity (i.e., abundance of ‘phytodetritus species’) and records of palaeoclimatic/palaeoceanographic proxies, suggesting that bentho-pelagic coupling (arrival of food on the seafloor with local surface productivity) might not have been straightforward in this region. Site 980 is located in the hydrodynamically active area of Feni Drift, and during the Holocene, currents might have winnowed and removed fine-grained organic matter, making it unavailable to benthic organisms. Alternatively, there may have been changes in remineralization and/or mid-water competition for food, so that the fraction of the organic flux that reached the seafloor may have varied. Holocene benthic foraminiferal assemblages thus reflect highly dynamic conditions in export productivity and arrival of organic matter at the seafloor.
•Increases in the seasonality of productivity (reflected in peaks in abundance of ‘phytodetritus species’ N. iridea, A. weddellensis, C. obtusa, and E. exigua) occur at 8.0 ka, 7.0 ka, 6.3–5.6 ka, 4.7 ka, 4.3–3.4 ka and 2.4 ka.•Benthic foraminifera reflect highly dynamic conditions in export productivity and arrival of organic matter at the seafloor in the NE Atlantic during the Holocene.•Bentho-pelagic coupling (arrival of organic matter at seafloor and surface productivity) might not be straightforward in this region.
A sea ice record for Barrow Strait in the Canadian Arctic Archipelago (CAA) is presented for the interval 10.0–0.4
cal. kyr BP. This Holocene record is based primarily on the occurrence of a sea ice ...biomarker chemical, IP
25, isolated from a marine sediment core obtained from Barrow Strait in 2005. A core chronology is based on
14C AMS dating of mollusc shells obtained from ten horizons within the core. The primary IP
25 data are compared with complementary proxy data obtained from analysis of other organic biomarkers, stable isotope composition of bulk organic matter, benthic foraminifera, particle size distributions and ratios of inorganic elements. The combined proxy data show that the palaeo-sea ice record can be grouped according to four intervals, and these can be contextualised further with respect to the Holocene Thermal Maximum (HTM). Spring sea ice occurrence was lowest during the early–mid Holocene (10.0–6.0
cal. kyr BP) and this was followed by a second phase (6.0–4.0
cal. kyr BP) where spring sea ice occurrence showed a small increase. Between 4.0 and 3.0
cal. kyr BP, spring sea ice occurrence increased abruptly to above the median and we associate this interval with the termination of the HTM. Elevated spring sea ice occurrences continued from 3.0 to 0.4
cal. kyr BP, although they were more variable on shorter timescales. Within this fourth interval, we also provide evidence for slightly lower and subsequently higher spring sea ice occurrence during the Mediaeval Warm Period and the Little Ice Age respectively. Comparisons are made between our proxy data with those obtained from other palaeo-climate and sea ice studies for the CAA.
Evolution of planktic organisms from benthic ancestors is commonly thought to represent unidirectional expansion into new ecological domains, possibly only once per clade. For foraminifera, this ...evolutionary expansion occurred in the Early-Middle Jurassic, and all living and extinct planktic foraminifera have been placed within 1 clade, the Suborder Globigerinina. The subsequent radiation of planktic foraminifera in the Jurassic and Cretaceous resulted in highly diverse assemblages, which suffered mass extinction at the end of the Cretaceous, leaving an impoverished assemblage dominated by microperforate triserial and biserial forms. The few survivor species radiated to form diverse assemblages once again in the Cenozoic. There have, however, long been doubts regarding the monophyletic origin of planktic foraminifera. We present surprising but conclusive genetic evidence that the Recent biserial planktic Streptochilus globigerus belongs to the same biological species as the benthic Bolivina variabilis, and geochemical evidence that this ecologically flexible species actively grows within the open-ocean surface waters, thus occupying both planktic and benthic domains. Such a lifestyle (tychopelagic) had not been recognized as adapted by foraminifera. Tychopelagic are endowed with great ecological advantage, enabling rapid recolonization of the extinction-susceptible pelagic domain from the benthos. We argue that the existence of such forms must be considered in resolving foraminiferal phylogeny.
Species assemblage composition of marine microfossils offers the possibility to investigate ecological and climatological change on time scales inaccessible using conventional observations. ...Planktonic foraminifera - calcareous zooplankton - have an excellent fossil record and are used extensively in palaeoecology and palaeoceanography. During the Last Glacial Maximum (LGM; 19,000 - 23,000 years ago), the climate was in a radically different state. This period is therefore a key target to investigate climate and biodiversity under different conditions than today. Studying LGM climate and ecosystems indeed has a long history, yet the most recent global synthesis of planktonic foraminifera assemblage composition is now nearly two decades old. Here we present the ForCenS-LGM dataset with 2,365 species assemblage samples collected using standardised methods and with harmonised taxonomy. The data originate from marine sediments from 664 sites and present a more than 50% increase in coverage compared to previous work. The taxonomy is compatible with the most recent global core top dataset, enabling direct investigation of temporal changes in foraminifera biogeography and facilitating seawater temperature reconstructions.
The Hatay Graben is one of three easternmost basins in the Mediterranean that preserve sediments that span the Miocene–Pliocene boundary, including gypsums from the Messinian Salinity Crisis (MSC). ...Here we integrate existing data and present new sedimentological and micropalaeontological data to investigate the palaeoenvironments of late Miocene to early Pliocene deposits and place this important area into a regional stratigraphic framework. Six sections are described along a ~W–E transect illustrating the key features of this time period. Late Miocene (Pre-MSC) sediments are characterised by open marine marls with a benthic foraminiferal fauna suggestive of water depths of 100–200m or less. Primary lower gypsum deposits are determined to be absent from the graben as sedimentological and strontium isotopes are characteristic of the Resedimented Lower Gypsums. The intervening Messinian erosion surface is preserved near the basin margins as an unconformity but appears to be a correlative conformity in the basin depocentre. No Upper Gypsums or ‘Lago Mare’ facies have been identified but available data do tentatively suggest a return to marine conditions in the basin prior to the Zanclean boundary. Sediments stratigraphically overlying the Messinian gypsums and marls are coarse-grained sandstones from coastal and Gilbert-type delta depositional environments. The Hatay Graben is not only strikingly similar to Messinian basins on nearby Cyprus but also to the overall model for the MSC, demonstrating the remarkable consistency of palaeoenvironments found in marginal basins across the region at this time. This research also raises questions as to the timing of the Mediterranean reflooding and the significance of the widespread mega-breccias of the resedimented gypsum deposits.
•We present a global biogeography and mtCO1 phylogeny for all atlantid morphospecies.•An updated biogeography for all morphospecies is constructed from museum collections.•Phylogeny of 437 new and 52 ...published sequences revealed 33 clades, 10 that are new.•Some new clades have unique morphological characters and may represent new species.•New clades have distinct distributions, suggesting narrow environmental tolerances.
The atlantid heteropods are regularly encountered, but rarely studied marine planktonic gastropods. Relying on a small (<14 mm), delicate aragonite shell and living in the upper ocean means that, in common with pteropods, atlantids are likely to be affected by imminent ocean changes. Variable shell morphology and widespread distributions indicate that the family is more diverse than the 23 currently known species. Uncovering this diversity is fundamental to determining the distribution of atlantids and to understanding their environmental tolerances. Here we present phylogenetic analyses of all described species of the family Atlantidae using 437 new and 52 previously published cytochrome c oxidase subunit 1 mitochondrial DNA (mtCO1) sequences. Specimens and published sequences were gathered from 32 Atlantic Ocean stations, 14 Indian Ocean stations and 21 Pacific Ocean stations between 35°N and 43°S. DNA barcoding and Automatic Barcode Gap Discovery (ABGD) proved to be valuable tools for the identification of described atlantid species, and also revealed ten additional distinct clades, suggesting that the diversity within this family has been underestimated. Only two of these clades displayed obvious morphological characteristics, demonstrating that much of the newly discovered diversity is hidden from morphology-based identification techniques. Investigation of six large atlantid collections demonstrated that 61% of previously described (morpho) species have a circumglobal distribution. Of the remaining 39%, two species were restricted to the Atlantic Ocean, five occurred in the Indian and Pacific oceans, one species was only found in the northeast Pacific Ocean, and one occurred only in the Southern Subtropical Convergence Zone. Molecular analysis showed that seven of the species with wide distributions were comprised of two or more clades that occupied distinct oceanographic regions. These distributions may suggest narrower environmental tolerances than the described morphospecies. Results provide an updated biogeography and mtCO1 reference dataset of the Atlantidae that may be used to identify atlantid species and provide a first step in understanding their evolutionary history and accurate distribution, encouraging the inclusion of this family in future plankton research.
Recent concern over the effects of ocean acidification upon calcifying organisms has highlighted the aragonitic shelled thecosomatous pteropods as being at a high risk. Both in-situ and laboratory ...studies have shown that an increased dissolved CO2 concentration, leading to decreased water pH and low carbonate concentration, causes reduced calcification rates and enhanced dissolution in the shells of living pteropods. In fossil records unaffected by post-depositional dissolution, this in-life shell dissolution can be detected. Here we present the first evidence of variations of in-life pteropod shell dissolution due to variations in surface water carbonate concentration during the Late Pleistocene by analysing the surface layer of pteropod shells in marine sediment cores from the Caribbean Sea and Indian Ocean. In-life shell dissolution was determined by applying the Limacina Dissolution Index (LDX) to the sub-tropical pteropod Limacina inflata. Average shell size information shows that high in-life dissolution is accompanied by smaller shell sizes in L. inflata, which may indicate a reduction in calcification rate. Comparison of the LDX profile to Late Pleistocene Vostok atmospheric CO2 concentrations, shows that in-life pteropod dissolution is closely associated to variations in past ocean carbonate saturation. This study confirms the findings of laboratory studies, showing enhanced shell dissolution and reduced calcification in living pteropods when surface ocean carbonate concentrations were lower. Results also demonstrate that oceanic pH levels that were less acidic and changing less rapidly than those predicted for the 21st Century, negatively affected pteropods during the Late Pleistocene.
•In-life dissolution of fossil pteropod shells was examined using the LDX scale.•Average shell diameter was used as an indicator of calcification rate.•LDX shows significant correlation to CO2 and surface water carbonate concentration.•Smaller, more corroded shells were found during interglacial periods.•Larger, pristine shells were found during glacial periods.
Ocean acidification causes biodiversity loss, alters ecosystems, and may impact food security, as shells of small organisms dissolve easily in corrosive waters. There is a suggestion that ...photosynthetic organisms could mitigate ocean acidification on a local scale, through seagrass protection or seaweed cultivation, as net ecosystem organic production raises the saturation state of calcium carbonate making seawater less corrosive. Here, we used a natural gradient in calcium carbonate saturation, caused by shallow‐water CO2 seeps in the Mediterranean Sea, to assess whether seaweed that is resistant to acidification (Padina pavonica) could prevent adverse effects of acidification on epiphytic foraminifera. We found a reduction in the number of species of foraminifera as calcium carbonate saturation state fell and that the assemblage shifted from one dominated by calcareous species at reference sites (pH ~8.19) to one dominated by agglutinated foraminifera at elevated levels of CO2 (pH ~7.71). It is expected that ocean acidification will result in changes in foraminiferal assemblage composition and agglutinated forms may become more prevalent. Although Padina did not prevent adverse effects of ocean acidification, high biomass stands of seagrass or seaweed farms might be more successful in protecting epiphytic foraminifera.
There is a suggestion that photosynthetic organisms could mitigate ocean acidification on a local scale. Here, we used a natural gradient in calcium carbonate saturation to assess whether seaweed that is resistant to acidification (Padina pavonica) could prevent adverse effects of acidification on epiphytic foraminifera. We found that the assemblage shifted from one dominated by calcareous species at reference sites (pH ~8.19) to one dominated by agglutinated foraminifera at elevated levels of CO2 (pH ~7.71).
Fewer than 1% of marine gastropod species live a holoplanktic life. Of these, the shelled heteropods of the family Atlantidae are among the most poorly understood. The atlantids potentially make up ...an important part of the ocean zooplankton, composing up to 69% of shelled holoplanktic gastropods in the Late Pleistocene to Recent fossil record. They are also likely to be at high risk from current and future global changes, including anthropogenic ocean acidification. However, due to their small size (<12 mm), difficulty of sampling and complicated morphology, we still lack key information about atlantid taxonomy and ecology. This makes it difficult to understand how important they are in the ocean foodweb and how they will be affected by environmental change. Although many studies have been carried out on the atlantids, these have generally been broad and unconnected. Here, we draw together this previous research, summarizing what is currently known about atlantid taxonomy, palaeontology, ecology and biogeography, and aiming to provide a foundation for future research on this group. The data indicate complex behaviours involving seasonal and vertical migration, and demonstrate extended geographical ranges, with implications for understanding the role of atlantids in the ocean foodweb and their sensitivity to environmental changes. This review highlights the urgent need for further taxonomic research on the atlantids, including molecular analysis, and for improved sampling techniques.
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