Laminated sediments provide a rare opportunity to examine seasonal-scale ocean/atmosphere variation during abrupt climate transitions. Seasonal-scale changes through the transition from Heinrich Stadial 5 to Greenland Interstadial 12 are recorded in a sediment core (MD02-2515) from the Guaymas Basin, Gulf of California. The laminated sediments of the full interstadial have the highest opal concentrations (59.6 wt % biogenic silica) of the entire 55 kyr sequence and contain monospecific concentrations of the tropical oceanic diatom Azpeitia nodulifera that record flux from exceptional bloom events. Enhanced silica supply was likely initiated from the Southern Ocean during Heinrich Stadial 5, when Southern Hemisphere warming, via the bipolar seesaw mechanism, led to increased upwelling around Antarctica and an increase in silica supply to Subantarctic Mode Water formation. The resulting pulse of silica-rich waters was rapidly transferred north to the Equatorial Undercurrent and thence via the subsurface Mexican Coastal Current to the Gulf of California. Overall, the sequence shows a resurgence in El Nino strength and an intensification of the North American Monsoon associated with Northern Hemisphere warming on the transition to Greenland Interstadial 12. Penetration of tropical waters to the Gulf was aided by El Nino events. Diatom production in the summer stratified waters was in the subsurface, tapping nutrients from the nutricline. Marine varves up to 9 mm thick record as many as 8 within-year flux events. Repeated summer flux events of actively reproducing diatoms in subsurface blooms were driven by recurrent intense monsoonal Gulf surge storms. Around 60% of A. nodulifera cells examined were actively dividing and every stage of the cell division cycle is represented. Other diatom species record renewed vigour of winter - spring upwelling associated with strengthening northwesterly winds as the North Pacific high migrated northward. The monsoon intensification, the resurgence in El Nino strength and the strengthened winter-spring northwesterlies were likely all driven by the reduction to a minimum extent of the Laurentide Ice Sheet in Greenland Interstadial 12. The changes recorded in this transition to a warm interstadial may serve as an indicator of future changes in the region driven by global warming.

The subsurface chlorophyll maximum (SCM) is increasingly recognised as an important but understudied locus of primary production particularly in shelf seas. Here we report the results of a 4 year, repeat station, summer sampling programme (2013 – 2016) of a seasonally recurrent SCM in the Western English Channel. Interannual variability in phytoplankton community structure and chlorophyll distribution and intensity was strongly related to water column stability at the depth interval of the SCM and also to water temperature. The phytoplankton community was statistically distinct in each year. High stability, as evidenced by large Richardson numbers and a well-developed strong thermocline appeared to favour the growth of larger dinoflagellates (autotrophs or mixotrophs) and diatoms. Such conditions led to development of the most intense SCMs and these were sometimes dominated by a single or a few key species most prominently in 2015 with near monospecific concentrations of the dinoflagellate Tripos fusus with average peak SCM chlorophyll concentrations of 7.3 ± 4.4 μg l-1. By contrast, in years with low water column stability and intermittent turbulence at the thermocline (2014, 2016) there was greater chlorophyll dispersal and less intense SCM. In these low stability conditions, red fluorescent nano-phytoplankton, such as naked dinoflagellates, chlorophytes and prymnesiophytes, made a greater contribution to the community, possibly as a result of the advantages that motility and enhanced light utilisation efficiency confer within an SCM exposed to turbulence. It is also likely that turbulence disrupted the stability required by the larger dinoflagellates and diatoms. Several of the key SCM taxa were absent from surface waters including the dinoflagellates Tripos fusus, Tripos lineatus, and most of the Rhizosolenia/ Proboscia diatoms, consistent with adaptations more suited to survival at depth in stratified waters. These traits include luxury nutrient uptake and storage and survival in low light (both groups) and mixotrophy (dinoflagellates). On the other hand, in 2013, diatoms including Pseudo-nitzschia spp. were abundant in both surface, SCM and bottom waters. The relatively cooler waters (11.6 - 12.1 °C on average in 2013 and 2016) were characterised by smaller diatoms (Chaetoceros spp. and Pseudo-nitzschia spp.) whereas the warmer waters (13.1 °C on average in 2014) contained larger diatoms (large Rhizosolenia spp., Lauderia annulata and Leptocylindrus danicus). There did not appear to be continuity of key species between years, other than for the dinoflagellate Tripos lineatus, which was significant in both 2013 and 2014 and present in 2015. In any given year, there was no correspondence between the key spring bloom phytoplankton species as monitored in the nearby Western Channel Observatory L4 station and the key SCM taxa.

Laminated diatomaceous sediments occur intermittently in the Bering Sea over the past 5 million years. A varve (annually deposited) origin for the laminae has been suggested, but there is currently no consensus. Here, we report results of a study of two laminated intervals dating from -528 ka and - 782 ka from IODP Site U1340 on the Bowers Ridge. We combine conventional micropaleontological methods with scanning electron microscope analysis that resolves the seasonal cycle of flux events recorded and demonstrates an annual origin for the laminae. Resting spores of Chaetoceros spp., and more rarely of Thalassiosira antarctica represent early spring blooms with the latter likely due to increased meltwater input. Diatom laminae containing concentrations of Shionodiscus trifultus, Thalassiosira spp., Actinocyclus curvulatus, and Neodenticula seminae, represent flux from the main spring-summer bloom episodes, with the latter indicating influx of seed populations from the North Pacific Alaskan Stream. Concentrations of Coscinodiscus spp. in the uppermost part of the diatom laminae represent "Fall Dump" sedimentation of these stratified-adapted diatoms in response to break down of summer stratification in autumn/early-winter storms. The lithogenic laminae represent mainly winter deposition and rare earth element analysis suggests provenance from the southern Bering Sea shelf and the Aleutian Arc. Productivity was high in the studied intervals with total mass fluxes around 5 times higher than modern values. Variation in lamina thickness and diatom composition contain periodicities of 2-8 years, as well as a bi-decadal variability likely related to influence of the Pacific Decadal Oscillation.

Marine phytoplankton form the base of marine food webs and are the driving force of the marine carbon cycle, so understanding the dynamics of their blooms is critical. While near-surface marine productivity (<10 m water depths) is extensively documented, that of the subsurface is less well characterised. Increasing evidence of the importance of subsurface chlorophyll maxima (SCM) and climatically driven increases in stratification of surface waters that promote SCM development call for improved sampling of the subsurface. To address this, we targeted the summer stratified waters of the Western English Channel, part of the NW European shelf seas, where SCM are commonly developed. In situ holography was applied to undertake the highest ever resolution, total water column, quantitative analysis of microplankton distribution, and demonstrated the importance of a SCM, co-located with the thermocline, dominated by a single species, the dinoflagellate Ceratium fusus. This species was dominant in the SCM over a wide area of the NW European shelf in the June/July 2015 study period and comprised up to 85% of the SCM biomass. Analysis of similarity and multivariate non-metric multidimensional scaling showed the phytoplankton community of the SCM to be statistically distinct from those of the surface and deep waters. Holography also revealed a fine scale layering of taxa at different levels within the SCM, likely reflecting ecological differences. Some taxa followed the peak abundance of C. fusus, while others reached maximum abundances immediately below or above the C. fusus maximum, suggesting the possible operation of exclusion mechanisms. Additionally, the detection of abundant aggregates located only within and beneath the SCM demonstrates the potential importance of this deep production for the export of carbon to the sea floor. Some predictions of phytoplankton productivity propose a shift to smaller cells in the more stratified oceans of the future resulting in declining production and export. Results presented here, however, contribute to a growing body of evidence that suggests, on the contrary, that key species among the larger celled/colonial, SCM-adapted diatoms and dinoflagellates may instead be selected in stratified conditions, driving increased production and export.

Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.

Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.

Many lakes undergo anthropogenically driven eutrophication and pollution leading to decreased water and sediment quality. These effects can enhance seasonally changing lake redox conditions that may concentrate potentially toxic elements. Here we report the results of a multi-method geochemical and sediment microfabric analysis applied to reconstruct the history of cultural eutrophication and pollution of the North and South Basins of Windermere, UK. Eutrophication developed from the mid-19th to the earliest 20th centuries. Enhanced lake productivity is indicated by increased sedimentary δ13C, and increased pollution by a higher concentration of metals (Pb, Hg, and As) in the sediment, likely enhanced by incorporation and adsorption to settling diatom aggregates, preserved as sedimentary laminae. In the South Basin, increasing sediment δ15N values occur in step with Zn, Hg, and Cu, linking metal enrichment to isotopically heavy nitrate (N) from anthropogenic sources. From around 1930, decreases in Mn and Fe-rich laminae indicate reduced deep-water ventilation, whereas periods of sediment anoxia increased, being most severe in the deeper North Basin. Strongly reducing sediment conditions promoted Fe and Mn reduction and Pb-bearing barite formation, hitherto only described from toxic mine wastes and contaminated soils. From 1980 there was an increase in indicators of bottom water oxygenation, although not to before 1930. But in the South Basin, the continued impacts of sewage are indicated by elevated sediment δ15N. Imaging and X-ray microanalysis using scanning electron microscopy has shown seasonal-scale redox mineralisation of Mn, Fe, and Ba related to intermittent sediment anoxia. Elevated concentrations of these metals and As also occur in the surficial sediment and provide evidence for dynamic redox mobilisation of potentially toxic elements to the lake water. Concentrations of As (up to 80 ppm), exceed international Sediment Quality Standards. This process may become more prevalent in the future with climate change driving lengthened summer stratification.

Many lakes in industrialised areas have undergone anthropogenically driven eutrophication and increases in pollution leading to decreased water and sediment quality. In some cases, these effects are enhanced by seasonally changing lake redox conditions that may act to concentrate potentially toxic elements sufficiently to exceed internationally recognised Sediment Quality Standards, impacting key species and jeopardizing water supply. A combined, geochemical and sediment microfabric analysis is applied to reconstruct the history of cultural eutrophication and pollution in the North and South Basins of Windermere, England’s largest natural lake. We also document a record of seismicity and link increased sedimentation rates and sediment instability. The onset and development of eutrophication in Windermere occurred from the mid-19th to the early 20th centuries. Raised lake productivity is indicated by an increase in sedimentary δ13C, and increased pollution by elevated sedimentary trace metals (Pb, Zn, Cu, Hg, and As), likely enhanced by incorporation and adsorption to settling diatom aggregates, preserved as sedimentary laminae. In the South Basin of the lake, contemporaneous increasing sediment δ15N values also occur in step with increasing Zn, Hg, Cu from this time, linking metal enrichment to the input of isotopically heavy nitrate (N) from anthropogenic sources including sewage. From around 1930, a decrease in Mn and Fe-rich laminae indicate reduced deep water ventilation, and increased incidence of sediment anoxia, being most intense in the deeper North Basin where benthic activity intermittently ceased. Strongly reducing conditions in the sediment promoted Fe and Mn reduction and the formation of unusual Pb-bearing barite, hitherto only described from toxic mine wastes and contaminated soils. In the North Basin cores a clay rich laminae dated 1979-1980 is shown to be a mass transport deposit linked to large scale slope failure likely caused by the 4.7 ML 1979 Carlisle earthquake. Slope failure was exacerbated by preconditioning principally by increased sedimentation as a result of anthropogenic activities. From 1980 there was a partial recovery in oxygenation with Mn and Fe rich laminae returning in some parts. But in the South Basin, the continued impacts of sewage discharge is indicated by elevated δ15N of organic matter. Imaging and X-ray microanalysis using scanning electron microscopy has enabled the identification of seasonal-scale redox mineralisation of Mn, Fe and Ba related to intermittent sediment anoxia. Elevated concentrations of Mn, Fe, Ba, and As also occur in the surficial sediment and provide evidence for dynamic redox mobilisation of potentially toxic elements that may be released to the lake waters. Concentrations of As, in particular, exceed international Sediment Quality Standards. These surface enrichments in As and other toxic elements may become more prevalent in the future with climate change driving lengthened summer stratification in the lake.

Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.

Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.

The Western English Channel is a seasonally stratified temperate coastal sea where a subsurface chlorophyll maximum (SCM) is typically detectable within the seasonal thermocline. The SCM often develops as a thin layer ( < 5 m) that may contain elevated concentrations of phytoplankton (subsurface chlorophyll maximum thin layer; SCMTL). During summer 2013 a study was conducted offshore of Falmouth, UK to assess spatial and short-term temporal variability in SCM thickness in relation to water column structure and physical conditions and to evaluate any associated changes in phytoplankton community structure. SCMTLs were observed in 18 of 52 vertical profiles, typically characterised by higher chlorophyll concentrations than broader SCMs. SCMTLs were generally associated with a 'stepped' thermocline, likely representing the presence of one or more shallow mixed layers forming above/within the seasonal thermocline, and related to increased stratification compared to broader SCMs. Pseudo-nitzschia was almost exclusively the dominant diatom taxon in SCMs, yet statistically distinct differences in community structure existed between SCMTLs and broader SCMs. Within the phytoplankton, the distinction was largely due to a greater biomass of Proboscia alata and other rhizosolenid diatoms, and the dinoflagellate Ceratium lineaturn in SCMTLs, and a smaller population of the diatom Chaetoceros spp. There was also a distinction amongst heterotrophic dinoflagellates, with enhanced biomass of Gyrodinium spp. in SCMTLs and a reduction in Diplopsalis lenticula. We propose that this observed difference resulted from promotion of phytoplankton better adapted to environmental conditions more specific to SCMTLs compared to broader SCMs. With more intense and prolonged stratification projected for the NW European shelf, there may be increased prevalence of SCMTLs and the associated larger-sized specialised taxa, with implications for increased carbon export. This study adds to a growing body of evidence of the importance of SCMTLs in coastal and shelf seas, and highlights the requirement for improved understanding of physical forcing and the ecology and physiology of key taxa, particularly as predicted changes in stratification could alter the role of SCM phytoplankton in a future influenced by climate change.

Annually laminated sediments (varves) provide excellent temporal resolution to study rapid environmental change, but are rare in the early part of the Last Termination (similar to 19-similar to 11.7 ka BP). We present a new >400 varve year (vyr) varve sequence in two floating parts from Windermere, a lake at the southern margin of the mountains of northwest England. This sequence records the final retreat of the Windermere glacier at the southern edge of the Lake District Ice Cap during the transition from Heinrich Stadial 1 (similar to 18-similar to 14.7 ka BP) into the Lateglacial Interstadial (similar to 14.7-similar to 12.9 ka BP). Laminated sediments from four lake cores from Windermere's northern and southern basins were investigated and shown to be varved. These sequences are integrated with seismic reflection evidence to reconstruct south-to-north deglaciation. Seismic and sedimentological evidence is consistent with gradual stepped ice retreat along the entire southern basin and into the northern basin between 255 and 700 vyr prior to the appearance of significant biota in the sediment that heralded the Lateglacial Interstadial, and had retreated past a recessional moraine (RM8) in the northern basin by 121 vyr prior to the interstadial. The Lateglacial interstadial age of this biota-bearing unit was confirmed by C-14-dating, including one date from the northernmost core of similar to 13.5 cal ka BP. A change in mineralogy in all four cores as the glacier retreated north of the Dent Group (the northernmost source of calcareous bedrock) and a decrease in coarse grains in the varves shows that the ice had retreated along the entire North Basin at similar to 70 vyr prior to the Lateglacial Interstadial. The estimated retreat rate is 70-114 m yr(-1) although buried De Geer moraines, if annual, may indicate retreat of 120 m yr(-1) with a >= 3 year stillstand at a recessional moraine halfway along the basin. The glacier then retreated north of the lake basin, becoming land-terminating and retreating at 92.5-49 m yr(-1). The northernmost core has a varve sequence ending at least 111 vyr after the other core chronologies, due to the increased proximity to remnant ice in the catchment uplands into the early Lateglacial Interstadial. We show that almost all of the glacier retreat in the Windermere catchment occurred before the abrupt warming at the onset of the Lateglacial Interstadial, in keeping with similar findings from around the Irish Sea Basin, and suggesting a similar retreat timescale for other radial valley glaciers of the Lake District Ice Cap. The seismic and core evidence also show the potential for a much longer varve chronology extending at least 400 and potentially over 1000 vyr further back into Heinrich Stadial 1 (18-14.7 ka BP), suggesting that glacier retreat in the Windermere valley initiated at least before 15.5 ka BP and perhaps 16 Ka BP. (C) 2019 The Authors. Published by Elsevier Ltd.

Models used to predict future ocean ecosystem and biogeochemical behaviour depend on simplified ecological frameworks allowing the definition of plankton functional types. Foremost among such frameworks has been the mandala of Margalef. His 1978 paper has been increasingly referred to in the past decade as simplified ecological schemes have been sought to help predict the effect of climate change on phytoplankton. However, the mandala is based on an understanding of the subject that is over 40 years old, when observational studies were largely limited to the coastal ocean and to near surface waters. Furthermore, most recent reproductions of the mandala are significant oversimplifications of Margalef's original. In these simplified mandala-type constructs, diatoms, in particular, have commonly been cast as a single plankton functional type that thrive in turbulent waters and decrease in abundance with increasing stratification. On this basis, it is widely predicted that diatom productivity and hence the effectiveness of the marine biological carbon pump will decrease with climate change that is driving increased stratification of the oceans. But Margalefs original took a more refined approach and depicted diatom genera that were adapted to more stratified conditions such as those characteristic of the subtropical oligotrophic gyres. If we now draw on the vast advances in observational oceanography of recent decades it is evident that diatoms may thrive, bloom and generate significant export even in the most intensely stratified and apparently oligotrophic conditions. Indeed, some diatom species have unique adaptations to such environments. We therefore suggest that it is time to abandon oversimplified schemes and recognize the diverse ecology of diatoms.

Lake sediments commonly contain detrital layers that record events such as floods or earthquakes, but these may be disturbed or partially destroyed by bioturbation. Here we use a novel combination of techniques to relate microscopic sediment fabric features to processes at the lake basin scale. X-radiography and micro-X-ray fluorescence analysis of cores are complemented by back-scattered electron imagery and energy-dispersive X-ray microanalysis of resin-embedded sediment. Together, the microfabric and geochemical methods enable the identification of clay layer mass transport deposits despite bioturbational mixing of the original end-members. Two cores with robust radionuclide chronologies contain correlative clay layers dated to 1979 (1974–1982) and 1979–1980 (1973–1986), respectively. These clay layers probably represent the distal turbidite generated by a major mass flow deposit identified from multi-beam swath bathymetry and sediment grab sampling. A probable trigger for the mass flow and associated turbidity current is the 4.7 M L 1979 Carlisle earthquake. The lake basin slope was probably preconditioned for failure by increased sedimentary biogenic gas production and sediment in-wash as a result of anthropogenic activities, coupled with sediment disruption and dredging. This study highlights the effectiveness of microstratigraphic techniques in the recognition and characterization of event layers in sediments where bioturbative disruption has occurred.

Laminated diatom-rich marine sediments from California and the Arctic Ocean provide a window into the seasonal climate and oceanography of the mid- and high-latitude Late Cretaceous. These remarkable shallow-buried sediments constitute palaeo-sediment traps that record exceptionally well-preserved sequential biogenic and lithogenic flux events. Many of the diatom laminae are composed of a few dominant taxa, and we use a species-based approach for palaeoecological interpretation. Contrary to many earlier interpretations, results indicate that both sites preserve a major flux of taxa adapted to exploit a strongly stratified ocean. The uppermost Maastrichtian Marca Shale of California records a seasonal cycle initiated with a spring bloom flux of diatom resting spores followed by a summer lithogenic sediment input likely driven by monsoonal storms providing river runoff and aeolian input. This is followed by a dominant diatom flux of species that thrived in the summer stratification in deep chlorophyll maxima and were sedimented in the fall when this stratification broke down. Dominant taxa comprising this group include Hemiaulus, Stephanopyxis, Stellarima and Rhizosolenia. The uppermost Campanian CESAR 6 core from the Arctic Alpha Ridge, records a spring bloom flux of resting spores followed by a more dominant summer and fall flux of diatom vegetative cells which were likely concentrated in subsurface summer blooms that generated a “summer export pulse” and by the breakdown of stratification in the fall that gave massive flux of deep chlorophyll maxima species in the fall dump. The dominance and diversity of Hemiaulus in the CESAR 6 core together with widespread evidence of N2-fixation may indicate that some diatom blooms were powered by intracellular N2-fixing cyanobacteria as in the modern oligotrophic ocean. Thin lenses of fine lithogenic sediment that occur mostly in the spring layer represent rafting by winter sea ice and support other evidence that suggests intermittent winter freezing in the Late Cretaceous Arctic.

Paleomagnetic secular variation (PSV) records serve as valuable independent stratigraphic correlation and dating tools for marine and terrestrial sediment sequences, and enhance knowledge of geomagnetic field dynamics. We present a new radiocarbon-dated record (WINPSV-12K) of Holocene geomagnetic secular variation from Windermere, updating the existing 1981 UK master PSV curve. Our analyses used continuous U-channel samples taken from the center of four sediment cores retrieved from Windermere in 2012. The natural remanent magnetization (NRM) of each U-channel was measured before and after stepwise alternating field (AF) demagnetization on a superconducting rock magnetometer at intervals of 0.5-cm or 1-cm. The NRM data reveal a stable and well-defined primary magnetization. Component declinations and inclinations estimated using Principal Component Analysis (PCA) of NRM data from the four Windermere cores correlate well on their independent radiocarbon age models. The four records were stacked using a sliding window bootstrap method, resulting in a composite Holocene PSV record (WINPSV-12K). On millennial timescales WINPSV-12K correlates well with other records from Western Europe and the northern North Atlantic to a resolution of similar to 1 kyr, given age uncertainties and spatial variability between records. WINPSV-12K also compares well to the CALS10k.2 and pfm9k.1a model predictions for Windermere. Key regionally-significant PSV inclination features of WINPSV-12K which correlate with other North Atlantic records include peaks at 5-6, 8.5, and 10 cal ka BP, and a trough at 7 cal ka BP. Key PSV declination features include the eastward swing from 5.5-2.3 cal ka BP followed by a major westward excursion at 2.3 cal ka BP, peaks at 11 and 7 cal ka BP, and troughs at 5.4 and 8.2 cal ka BP, with the caveat that an estimated magnetic lock-in delay of at least 100-200 yr is present. PSV variations on 1-3 kyr timescales are interpreted to represent strengthening and weakening of the North American versus the Siberian and European-Mediterranean high-latitude flux lobes, based on the close similarities between the North Atlantic regional records and the antiphase existing in the East Asian Stack record and the North East Pacific inclination stack. WINPSV-12K provides a regionally-important new PSV reference curve whose prominent features may serve as stratigraphic markers for North Atlantic paleo-records. (C) 2017 The Authors. Published by Elsevier B.V.

The fossil species Trochosira polychaeta Strelnikova, exhibits a wide range of preservational states that has led to contrasting interpretations with regard to its resting stage or vegetative cell status. Within shallow-buried, well-preserved diatomites from the Alpha Ridge of the Arctic Ocean, a continuum of dissolution effects is documented and a vegetative cell status is clearly indicated. The chains are formed by a central linking process, but complex marginal structures also constitute a complementary linking mechanism. The double linkage may have supported the integrity of the colonial chains and provided a mechanism for enhanced nutrient uptake. The presence of two distinct types of linking might also represent a stage in a transition from the Cretaceous, when central linking structures were common, through the Cenozoic to the modern, with more common linking through marginal structures.