Re-evaluation and extension of the Marine Isotope Stage 5 tephrostratigraphy of the Faroe Islands region: The cryptotephra record

PMA, SMD, WENA and NJGP are supported by NERC through the SMART project (NE/F020600/1, NE/F02116X/1, NE/F021445/1). The research leading to the results for the MIS 4 and 5a tephra horizons has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement n° [259253]. PMA, SMD and NJGP acknowledge the support of the Climate Change Consortium of Wales (C3W). JB is funded by the Research Council of Norway through the INTERACT project (project no. 221999).Abstract Previous studies of marine sequences from the Faroe Islands region have identified a series of coarse-grained tephra horizons deposited during Marine Isotope Stage (MIS) 5. Here we reassess the MIS 5 tephrostratigraphy of the Faroe Islands region and focus on the cryptotephra deposits preserved within the fine-grained fraction of marine core LINK 16. We also extend the record to encompass the late MIS 6 and early MIS 4 periods. A density separation technique, commonly used for tephra investigations in lacustrine settings but rarely applied to marine sediments, is utilised to explore the fine-grained material and EPMA and LA-ICP-MS are employed to determine the major and trace element composition of individual tephra shards. In total, 3 basaltic and 3 rhyolitic Icelandic cryptotephra deposits with homogeneous geochemical compositions are identified — all of which have the potential to act as isochronous tie-lines. Geochemical results highlight that the Grímsvötn volcanic system of Iceland is the predominant source of the basaltic horizons and the Öraefajökull or Torfajökull systems are the likely sources of the rhyolitic deposits. Three of the horizons have been previously recognised in Faroe Islands region marine sequences, with two of these deposits traceable into a Norwegian Sea sequence. An early MIS 4 rhyolitic horizon is the most widespread deposit as it can be traced into the Norwegian Sea and to the south into a record from the Rockall Trough. Basaltic and rhyolitic horizons deposited during late MIS 6 have not been recognised in other sequences and represent new additions to the regional tephrostratigraphy.Publisher PDFPeer reviewe

Deep sea ventilation of the northeastern Atlantic during the last 15,000 years.

Sea surface temperature and salinity estimates reconstructed from a core (56/-10/36) collected on the. Barra Fan, northwest Scotland (56 degrees 43 'N, 09 degrees 19 'W; water depth 1320 m) show a series of rapid oscillations during the last deglacial period that are very similar to those observed in the delta O-18 records from Greenland ice cores. These records indicate that the transport of heat and salt toward the Nordic Seas was highest during the Bolling period.A nearby deeper water core (57/-11/59) on the distal margin of the Barra Fan (57 degrees 01 'N, 10 degrees 01 'W, water depth 2089 m) allows us to study the response of the delta C-13 record of the benthic foraminifera Cibicidoides wuellerstorfi through the deglacial interval at a century/decadal scale. By comparing the sea surface temperature, salinity and benthic records at this site with other Atlantic Ocean records, we evaluate the timing of deep sea ventilation with changes in surface water characteristics. The benthic delta C-13 evidence suggests that NADW formation strengthened during the Bolling-Allerod period and ventilation was at least as strong as it has been for much of the Holocene. Maximum deep water formation was essentially coincident with the maximum northward transport of heat and salt, but predates the transition in delta C-13 Which is recorded in the deep western Atlantic. Deep water ventilation of this site was reduced during the Younger Dryas period. (C) 2001 Elsevier Science B.V. All rights reserved.</p

The Distribution of Benthic Foraminifera in the Celtic Sea: The Significance of Seasonal Stratification

Seasonal stratification is an important phenomenon in tidally-stirred shelf seas, influencing biological productivity, sedimentation rates, the organic content of shelf sediments, and the climate of surrounding landmasses. Previous micropaleontological and stable isotopic investigation investigation of a Holocene sequence from the Celtic Sea suggests that benthic foraminiferal distributions are linked to the physical and biological oceanographic characteristics associated with stratification. We have tested this hypothesis by analyzing the living and dead foraminiferal faunas from surface samples collected during across-frontal cruises during the summers of 1995 and 1996. Foraminiferal and environmental data for 56 samples are presented. Live and dead foraminiferal data were analyzed by factor analysis and, along with the environmental data, canonical correspondence analysis (CCA). Four distinct assemblages were identified from factor analysis of the live data: (1) a frontal assemblage characterized by Stainforthia fusiformis, (2) a mixed water assemblage characterized by Cibicides lobatulus, Textularia bockii, Spiroplectammina wrightii, Ammonia batavus and Quinqueloculina seminulum, (3) a stratified assemblage characterized by Bulimina marginata, Hyalinea balthica, Adercotryma wrighti and Nonionella turgida, and (4) an eastern assemblage dominated by Bulimina gibba, Elphidium excavatum and Eggerelloides scaber. Factor analysis of the dead data reproduces all groupings except the frontal assemblage. These data therefore support interpretations based on earlier stratigraphic data, and highlight the significance of benthic foraminifera as faunal indicators of paleostratification in shelf seas. The distributions also support predicted cross-frontal transfer of nutrients and the existence of surface converging circulation cells. Statistical analyses indicate the significance of unmeasured ecological variables which we speculate might be food supply, and oxygen concentration of bottom and sediment pore waters

Stable isotopic analyses of modern benthic foraminifera from seasonally stratified shelf seas:d isequilibria and the 'seasonal effect'

Previously published stable isotopic data on benthic foraminiferal species from a Holocene sequence in the Celtic Sea have been interpreted in terms of the progressive replacement of a tidally mixed by a stratified water mass. Offsets in the δ18O data between Ammonia batavus and Quinqueloculina seminulum were attributed to a ‘seasonal effect’ in which these two species were hypothesized to have calcified at different times of the year. The aims of this study were to test the hypotheses (1) that benthic foraminiferal stable isotope records from across the Celtic Sea front reflect seasonal stratification and (2) that offsets in the oxygen isotope record between different species are the result of the postulated seasonal effect. Hypothesis 1 was tested through investigation of live and dead benthic foraminiferal and bottom-water δ18O and δ13C sampled in transects across the Celtic Sea front from mixed through frontal to stratified water masses. Measurements of bottom-water salinity enabled a mixing-line equation to be developed for this area enabling quantitative reconstructions of bottom-water temperature from the isotopic data. Samples from stratified settings are characterized by heavier δ18Oforam and lighter δ13Cforam values than the mixed samples. Offsets in δ18Oforam between A. batavus and Q. seminum support the notion of the seasonal effect. A. batavus produces values close to equilibrium while Q. seminulum overestimates temperature by up to 2°C and this might explain some of the offset observed between the two species observed in the palaeodata. Comparison of the δ18Ofoarm data with measured seasonal temperature cycles from mixed and stratified localities in the Celtic Sea demonstrates that, while most foraminifera calcify during the summer months, different species calcify at, or are preserved from, different times within this warm part of the seasonal cycle; Q. seminulum calcifies during September when peak bottom-water temperatures occur, while A. batavus calcifies during September in stratified localities, but during spring or early summer in mixed localities. This study confirms the interpretation of the δ18O palaeodata from the Celtic Sea as a palaeostratification record and demonstrates that δ18O data from shelf-sea cores can be used to supplement benthic foraminiferal assemblages as a tool for reconstructing the long-term dynamics of seasonal stratification

Clarifying the role of inorganic carbon in blue carbon policy and practice

Since the term “blue carbon” was coined by the report of Nellerman et al. (2009) the marine carbon cycle has firmly entered the realm of marine policy alongside its terrestrial neighbour, “green carbon” (Crooks et al., 2018). Many marine policy decisions rely on accurate information concerning the stocks of blue carbon in a region, the annual sequestration rates associated with those stocks and the threats posed to those stocks by human activities, and especially recently by bottom-trawling (e.g., Sala et al., 2021). Hence policy officials are reliant on accurate blue carbon scientific advice. However, at the present moment there is one topic that is contributing confusion to policy-science understanding, and that is the topic of organic vs. inorganic carbon. The aim of this short note is to clarify the differences between these two types of blue carbon and to recommend how they are treated in policy formulation and the provision of scientific advice.PostprintPeer reviewe

Provenance of North Atlantic ice-rafted debris during the last deglaciation--A new application of U-Pb rutile and zircon geochronology

Understanding the provenance of ice-rafted debris (IRD) provides a means to link the behavior of individual ice sheets to proxy records of climate change. Here we present a new approach to determining IRD provenance using U-Pb geochronology of detrital minerals rutile and zircon. We characterize potential source regions from Scotland using detrital rutile from modern fluvial systems, and demonstrate that their unimodal rutile U-Pb ages reflect the timing of the last amphibolite facies metamorphism of the source rocks, imparting a distinctive source signature. Contrasts between these spectra and the bimodal IRD (ca. 470 Ma and ca. 1800–2000 Ma) rutile age signatures rule out Scotland as the sole source and suggest a Laurentian contribution; IRD zircon ages further support this view. U-Pb mineral dating has the potential to provide new insight on IRD provenance, because it allows linkage between IRD and individual source terranes based on their differing magmatic and tectonothermal histories. The occurrence of Laurentian-sourced IRD proximal to Scotland demonstrates widespread and rapid dispersal of debris across the subpolar North Atlantic during the Older Dryas cold oscillation, and implicates the Atlantic meridional overturning circulation as a control. This highlights the sensitivity of some IRD records to rapid climate change during the last deglaciation and supports the interpretation of Heinrich events as time-parallel marker horizons

The synchronization of palaeoclimatic events in the North Atlantic region during Greenland Stadial 3 (ca 27.5 to 23.3kyr b2k)

Two high resolution marine sediment cores located 83 km apart in the NE Atlantic have been studied: MD95-2006 (Barra Fan; 57°01.82 N, 10°03.48 W; 2120 m water depth) and MD04-2822 (Rockall Trough; 56°50.54 N, 11°22.96 W; 2344 m water depth). The records are anchored to the NGRIP ice core stratigraphy and GICC05 chronology by the presence of geochemically characterized Fugloyarbanki tephra and further tested by radiocarbon age control. Replicated sea surface temperature (SST) records show evidence for an abrupt and short-lived warming within Greenland Stadial (GS)-3, to which we tentatively assign an age of ca 25.6–24.8 kyr GICC05 b2k. Based on these and another marine palaeoclimate record (LINK17) from the Faroe-Shetland Channel, we propose a new three-fold event stratigraphy for GS-3 within the North East Atlantic region. The recognition of this warming event within GS-3 in NE Atlantic SST records demonstrates that such events may not readily be identified within the coldest stadials of the Greenland ice cores, highlights the need for carefully constructed event stratigraphies (independently tested by the use of tephra isochrones and radiocarbon) and illustrates pervasive millennial-scale climate variability of the North Atlantic region (Dansgaard-Oeschger (D/O) events) is deeply embedded in the dynamics of Atlantic Meridional Overturning Circulation (AMOC)