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Cenozoic evolution of the Antarctic ice sheets is thought to be driven primarily by long-term changes in radiative forcing, but the tectonic evolution of Antarctica may also have played a substantive role. While deep-sea foraminiferal oxygen isotope records provide a combined measure of global continental ice volume and ocean temperature, they do not provide direct insights into non-radiative influences on Antarctic Ice Sheet dynamics. Here we present an Antarctic compilation of Cenozoic upper-ocean temperature for the Ross Sea and offshore Wilkes Land, generated by membrane lipid distributions from archaea. We find trends of ocean temperature, atmospheric carbon dioxide and oxygen isotopes largely co-vary. However, this relationship is less clear for the late Oligocene, when high-latitude cooling occurred despite interpretation of oxygen isotopes suggesting global warming and ice-volume loss. We propose this retreat of the West Antarctic Ice Sheet occurred in response to a tectonically driven marine transgression, with warm surface waters precluding marine-based ice-sheet growth. Marine ice-sheet expansion occurred only when ocean temperatures further cooled during the Oligocene–Miocene transition, with cold orbital conditions and low atmospheric carbon dioxide. Our results support a threshold response to atmospheric carbon dioxide, below which Antarctica’s marine ice sheets grow, and above which ocean warming exacerbates their retreat.

It has been hypothesized that global temperature trends are tightly linked to tropical thermocline depth, and that thermocline shoaling played a crucial role in the intensification of late Pliocene Northern Hemisphere glaciation. The Pliocene thermocline evolution in the Pacific Ocean is well documented and supports this hypothesis, but thermocline records from the tropical Atlantic Ocean are limited. We present new planktonic foraminiferal Mg/Ca, δ18O, and δ13C records from the late Pliocene interval at Ocean Drilling Program Site 959 in the Eastern Equatorial Atlantic (EEA), which we use to reconstruct ocean temperatures and relative changes in salinity and thermocline depth. Data were generated using surface-dwelling Globigerinoides ruber and subsurface-dwelling Neogloboquadrina dutertrei. Reduced gradients between the surface and subsurface records indicate deepening of the EEA thermocline at the end of the mid-Piacenzian Warm Period (mPWP; ∼ 3.3–3.0 Ma). We connect our late Pliocene records to previously published early Pliocene δ18O data from Site 959 and compare these to the Site 1000 in the Caribbean Sea. Over the course of the Pliocene, thermocline changes in the EEA and Caribbean Sea follow similar patterns, with prominent step-wise thermocline deepening between ∼ 5.5 and 4.0 Ma and gradual shoaling up to the mPWP, followed by minor deepening at the end of the mPWP. The tropical thermocline depth evolution of the tropical Atlantic differs from the Pacific, which is characterized by gradual basin-wide shoaling across the Pliocene. These results potentially challenge the hypothesized link between tropical thermocline depth and global climate. The mechanisms behind the periodically divergent Pacific and Atlantic thermocline movements remain speculative. We suggest that they are related to basin geometry and heterogenous temperature evolutions in regions from where thermocline waters are sourced. A positive feedback loop between source region temperature and tropical cyclone activity may have amplified tropical thermocline adjustments.

This version of the article has been accepted for publication, after peer review and is subject to Springer Nature’s AM terms of use, but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available online at https://doi.org/10.1038/s41586-021-04148-0. Early to Middle Miocene sea-level oscillations of approximately 40–60 m estimated from far-field records1,2,3 are interpreted to reflect the loss of virtually all East Antarctic ice during peak warmth2. This contrasts with ice-sheet model experiments suggesting most terrestrial ice in East Antarctica was retained even during the warmest intervals of the Middle Miocene4,5. Data and model outputs can be reconciled if a large West Antarctic Ice Sheet (WAIS) existed and expanded across most of the outer continental shelf during the Early Miocene, accounting for maximum ice-sheet volumes. Here we provide the earliest geological evidence proving large WAIS expansions occurred during the Early Miocene (~17.72–17.40 Ma). Geochemical and petrographic data show glacimarine sediments recovered at International Ocean Discovery Program (IODP) Site U1521 in the central Ross Sea derive from West Antarctica, requiring the presence of a WAIS covering most of the Ross Sea continental shelf. Seismic, lithological and palynological data reveal the intermittent proximity of grounded ice to Site U1521. The erosion rate calculated from this sediment package greatly exceeds the long-term mean, implying rapid erosion of West Antarctica. This interval therefore captures a key step in the genesis of a marine-based WAIS and a tipping point in Antarctic ice-sheet evolution

During the so-called Messinian Salinity Crisis (MSC: 5.97-5.33 Myr ago), reduced exchange with the Atlantic Ocean caused the Mediterranean to develop into a “saline giant” wherein ~1 million km3 of evaporites (gypsum and halite) were deposited. Despite decades of research it is still poorly understood exactly how and where in the water column these evaporites formed. Gypsum formation commonly requires enhanced dry conditions (evaporation exceeding precipitation), but recent studies also suggested major freshwater inputs into the Mediterranean during MSC-gypsum formation. Here we use strontium isotope ratios of ostracods to show that low-saline water from the Paratethys Seas actually contributed to the precipitation of Mediterranean evaporites. This apparent paradox urges for an alternative mechanism underlying gypsum precipitation. We propose that Paratethys inflow would enhance stratification in the Mediterranean and result in a low-salinity surface-water layer with high Ca/Cl and SO4/Cl ratios. We show that evaporation of this surface water can become saturated in gypsum at a salinity of ~40, in line with salinities reported from fluid inclusions in MSC evaporites.

The study of Burano paleo-lagoon&mdash, Wetland of International Value, has allowed us to better define and extend the reconstruction of the Holocene paleoenvironmental evolution of the paleo-lagoons previously studied, located on the Tyrrhenian coast in central Italy. The investigated area is located in Southern Tuscany near the Burano Lake. The area was investigated by means of field surveys, historical maps, 16 coring, sedimentological, palynological and microfaunal analyses (foraminifera and ostracods), combined with robust geochronological control provided by 52 datings (14C and OSL). The study allowed us to reconstruct the environmental and morphological evolution of the Burano paleo-lagoon during the last 8000 years and to hypothesize a Rise Sea Level (RSL) curve. In this context, 5 main evolutionary phases have been recognized. (1) before 7.5 ka BP in the southern-eastern part, an open lagoon developed, (2) ~6 ka BP a barrier-lagoon system develops throughout the entire area and the lagoon progressively changed from open to closed one, (3) ~5 ka BP the width of the lagoon increases and a lacustrine facies appears along the entire axis of the coastal basin, (4) ~4 ka BP the lacustrine facies shows a discontinuous distribution respect to the previous phase, (5) during the last 4 ka the lacustrine facies disappear and the lagoon turns into a wetland area.

The study of Burano paleo-lagoon-Wetland of International Value, has allowed us to better define and extend the reconstruction of the Holocene paleoenvironmental evolution of the paleo-lagoons previously studied, located on the Tyrrhenian coast in central Italy. The investigated area is located in Southern Tuscany near the Burano Lake. The area was investigated by means of field surveys, historical maps, 16 coring, sedimentological, palynological and microfaunal analyses (foraminifera and ostracods), combined with robust geochronological control provided by 52 datings (14C and OSL). The study allowed us to reconstruct the environmental and morphological evolution of the Burano paleo-lagoon during the last 8000 years and to hypothesize a Rise Sea Level (RSL) curve. In this context, 5 main evolutionary phases have been recognized. (1) before 7.5 ka BP in the southern-eastern part, an open lagoon developed; (2) ~6 ka BP a barrier-lagoon system develops throughout the entire area and the lagoon progressively changed from open to closed one; (3) ~5 ka BP the width of the lagoon increases and a lacustrine facies appears along the entire axis of the coastal basin; (4) ~4 ka BP the lacustrine facies shows a discontinuous distribution respect to the previous phase; (5) during the last 4 ka the lacustrine facies disappear and the lagoon turns into a wetland area. © 2020 by the authors.

The morphology of dinoflagellate cysts (dinocysts) is related not only to the genetics of the motile dinoflagellate from which it derives, but is also dependent on a range of environmental factors including salinity, temperature and nutrient status. Although this knowledge improves our understanding of the drivers behind dinocyst morphological variations, it makes the taxonomy governing their description somewhat complex. In basins such as the Black Sea, where environmental change can be extreme and occurs on relatively short (millennial) timescales, taxonomy becomes particularly challenging. Morphological continua can be observed between described forms, displaying a large range of intermediate phenotypes that do not necessarily correspond to any genetic difference. As these morphological nuances may preserve information about palaeoenvironments, it is important to find a systematic method of characterising morphotypes. Here, we show a dinocyst matrix within which dinocysts are described according to their similarity to (or difference from) described forms based on key descriptive parameters. In the example set out here, cyst shape and degree of process and/or ectophragm development are taken as two key parameters in Pyxidinopsis psilata and Spiniferites cruciformis, and can allow the description of intermediate forms even though the definitions do not overlap. We review some frequently occurring morphotypes and propose that using matrices to show the gradual variation between endmember forms is the most pragmatic approach until cyst–theca studies and genetic sequencing can be used to demonstrate relationships between genotypes and morphotypes. As prior studies propose salinity to be a primary driver of intraspecific variability, the endmembers presented may represent salinity extremes within an overall brackish environment. Although we cannot assign each morphotype to a value or a range of an environmental parameter (e.g. salinity) as the different morphotypes can occur in the same sample, using this matrix allows preservation of information about morphological variability without creating taxonomic categories that are likely to require alteration if genetic evidence becomes available.

Early Eocene global climate was warmer than much of the Cenozoic and was punctuated by a series of transient warming events or ‘hyperthermals’ associated with carbon isotope excursions when temperature increased by 4–8 °C. The Paleocene-Eocene Thermal Maximum (PETM, ~55 Ma) and Eocene Thermal Maximum 2 (ETM2, 53.5 Ma) hyperthermals were of short duration (

During the last glacial period, climate conditions in the North Atlantic region were determined by the alternation of relatively warm interstadials and relatively cool stadials, with superimposed rapid warming (Dansgaard‐Oeschger) and cooling (Heinrich) events. So far little is known about the impact of these rapid climate shifts on the seasonal variations in sea surface temperature (SST) within the North Atlantic region. Here, we present a high‐resolution seasonal SST record for the past 152 kyrs derived from Integrated Ocean Drilling Program “Shackleton” Site U1385, offshore Portugal. Assemblage counts of dinoflagellates cysts (dinocysts) in combination with a modern analog technique (MAT), and regression analyses were used for the reconstructions. We compare our records with previously published SST records from the same location obtained from the application of MAT on planktonic foraminifera. Our dinocyst‐based reconstructions confirm the impression of the Greenland stadials and interstadials offshore the Portuguese margin and indicate increased seasonal contrast of temperature during the cold periods of the glacial cycle (average 9.0 °C, maximum 12.2 °C) with respect to present day (5.1 °C), due to strong winter cooling by up to 8.3 °C. Our seasonal temperature reconstructions are in line with previously published data, which showed increased seasonality due to strong winter cooling during the Younger Dryas and the Last Glacial Maximum over the European continent and North Atlantic region. In addition, we show that over longer time scales, increased seasonal contrasts of temperature remained characteristic of the colder phases of the glacial cycle., Key Points New high‐resolution dinocyst‐based summer and winter SST record from IODP “Shackleton” Site U1385 for the last 150 kyrs is presentedDinocyst‐based SST confirms the D‐O cycles and HEs at Site U1385Increased seasonal contrast of SST (up to 12 degree C) during cold periods of the glacial cycle related to strong winter cooling is shown

The marine-based West Antarctic Ice Sheet (WAIS) is currently retreating due to shifting wind-driven oceanic currents that transport warm waters toward the ice margin, resulting in ice shelf thinning and accelerated mass loss of the WAIS. Previous results from geologic drilling on Antarctica's continental margins show significant variability in marine-based ice sheet extent during the late Neogene and Quaternary. Numerical models indicate a fundamental role for oceanic heat in controlling this variability over at least the past 20 My. Although evidence for past ice sheet variability has been collected in marginal settings, sedimentologic sequences from the outer continental shelf are required to evaluate the extent of past ice sheet variability and the associated oceanic forcings and feedbacks. International Ocean Discovery Program Expedition 374 drilled a latitudinal and depth transect of five drill sites from the outer continental shelf to rise in the eastern Ross Sea to resolve the relationship between climatic and oceanic change and WAIS evolution through the Neogene and Quaternary. This location was selected because numerical ice sheet models indicate that this sector of Antarctica is highly sensitive to changes in ocean heat flux. The expedition was designed for optimal data-model integration and will enable an improved understanding of the sensitivity of Antarctic Ice Sheet (AIS) mass balance during warmer-than-present climates (e.g., the Pleistocene "super interglacials," the mid-Pliocene, and the late early to middle Miocene). The principal goals of Expedition 374 were to • Evaluate the contribution of West Antarctica to far-field ice volume and sea level estimates; • Reconstruct ice-proximal atmospheric and oceanic temperatures to identify past polar amplification and assess its forcings and feedbacks; • Assess the role of oceanic forcing (e.g., sea level and temperature) on AIS stability/instability; • Identify the sensitivity of the AIS to Earth's orbital configuration under a variety of climate boundary conditions; and • Reconstruct eastern Ross Sea paleobathymetry to examine relationships between seafloor geometry, ice sheet stability/instability, and global climate. To achieve these objectives, we will • Use data and models to reconcile intervals of maximum Neogene and Quaternary Antarctic ice advance with far-field records of eustatic sea level change; • Reconstruct past changes in oceanic and atmospheric temperatures using a multiproxy approach; • Reconstruct Neogene and Quaternary sea ice margin fluctuations in datable marine continental slope and rise records and correlate these records to existing inner continental shelf records; • Examine relationships among WAIS stability/instability, Earth's orbital configuration, oceanic temperature and circulation, and atmospheric pCO 2 ; and • Constrain the timing of Ross Sea continental shelf overdeepening and assess its impact on Neogene and Quaternary ice dynamics. Expedition 374 was carried out from January to March 2018, departing from Lyttelton, New Zealand. We recovered 1292.70 m of high-quality cores from five sites spanning the early Miocene to late Quaternary. Three sites were cored on the continental shelf (Sites U1521, U1522, and U1523). At Site U1521, we cored a 650 m thick sequence of interbedded diamictite, mudstone, and diatomite, penetrating the Ross Sea seismic Unconformity RSU4. The depositional reconstructions of past glacial and open-marine conditions at this site will provide unprecedented insight into environmental change on the Antarctic continental shelf during the early and middle Miocene. At Site U1522, we cored a discontinuous upper Miocene to Pleistocene sequence of glacial and glaciomarine strata from the outer shelf, with the primary objective to penetrate and date seismic Unconformity RSU3, which is interpreted to represent the first major continental shelf-wide expansion and coalescing of marine-based ice streams from both East and West Antarctica. At Site U1523, we cored a sediment drift located beneath the westerly flowing Antarctic Slope Current (ASC). Cores from this site will provide a record of the changing vigor of the ASC through time. Such a reconstruction will enable testing of the hypothesis that changes in the vigor of the ASC represent a key control on regulating heat flux onto the continental shelf, resulting in the ASC playing a fundamental role in ice sheet mass balance. We also cored two sites on the continental slope and rise. At Sit e U1524, we cored a Plio-Pleistocene sedimentary sequence on the continental rise on the levee of the Hillary Canyon, which is one of the largest conduits of Antarctic Bottom Water delivery from the Antarctic continental shelf into the abyssal ocean. Drilling at Site U1524 was intended to penetrate into middle Miocene and older strata but was initially interrupted by drifting sea ice that forced us to abandon coring in Hole U1524A at 399.5 m drilling depth below seafloor (DSF). We moved to a nearby alternate site on the continental slope (U1525) to core a single hole with a record complementary to the upper part of the section recovered at Site U1524. We returned to Site U1524 3 days later, after the sea ice cleared. W e then cored Hole U1524C with the rotary core barrel with the intention of reaching the target depth of 1000 m DSF. However, we were forced to terminate Hole U1524C at 441.9 m DSF due to a mechanical failure with the vessel that resulted in termination of all drilling operations and a return to Lyttelton 16 days earlier than scheduled. The loss of 39% of our operational days significantly impacted our ability to achieve all Expedition 374 objectives as originally planned. In particular, we were not able to obtain the deeper time record of the middle Miocene on the continental rise or abyssal sequences that would have provided a continuous and contemporaneous archive to the high-quality (but discontinuous) record from Site U1521 on the continental shelf. The mechanical failure also meant we could not recover sediment cores from proposed Site RSCR-19A, which was targeted to obtain a high-fidelity, continuous record of upper Neogene and Quaternary pelagic/hemipelagic sedimentation. Despite our failure to recover a shelf-to-rise transect for the Miocene, a continental shelf-to-rise transect for the Pliocene to Pleistocene interval is possible through comparison of the high-quality records from Site U1522 with those from Site U1525 an d legacy cores from the Antarctic Geological Drilling Project (ANDRILL).

Next to atmospheric CO2 concentrations, iceproximal oceanographic conditions are a critical factor for

Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23-14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3-4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO2. These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene.

Several episodes of abrupt and transient warming, each lasting between 50,000 and 200,000 years, punctuated the long-term warming during the Late Palaeocene and Early Eocene (58 to 51 Myr ago) epochs1,2. These hyperthermal events, such as the Eocene Thermal Maximum 2 (EMT2) that took place about 53.5 Myr ago2, are associated with rapid increases in atmospheric CO2 content. However, the impacts of most events are documented only locally86. Here we show, on the basis of estimates from the TEX 86 ′ proxy, that sea surface temperatures rose by 3-5 C in the Arctic Ocean during the EMT2. Dinoflagellate fossils demonstrate a concomitant freshening and eutrophication of surface waters, which resulted in euxinia in the photic zone. The presence of palm pollen implies5 that coldest month mean temperatures over the Arctic land masses were no less than 8 C, in contradiction of model simulations that suggest hyperthermal winter temperatures were below freezing6. In light of our reconstructed temperature and hydrologic trends, we conclude that the temperature and hydrographic responses to abruptly increased atmospheric CO2 concentrations were similar for the ETM2 and the better-described Palaeocene-Eocene Thermal Maximum7,8, 55.5 Myr ago. © 2009 Macmillan Publishers Limited. All rights reserved.

The Cenozoic sedimentary record of the central Arctic Ocean recovered during the Arctic Coring Expedition (ACEX) Integrated Ocean Drilling Program (IODP) Expedition 302 contains a new dinoflagellate cyst genus, Arcticacysta, assignable to the Peridiniales. Two different species are here formally described, Arcticacysta backmanii and A. moraniae gen. et sp. nov. Both species have a combination archeopyle, formed by the loss of several plates. In A. backmanii the archeopyle involves three apical (2’-4’) and three intercalary (1a-3a) plates. In A. moraniae the archeopyle is formed by the loss of four apical (1’-4’) and three intercalary (1a-3a) plates. The species differ in size and in the wall structure. A. backmanii has a microreticulate wall and is relatively large, whereas A. moraniae is smaller and with spinose wall. Their lowest occurrence in the ACEX core lies at the base of subunit 1/5 (core M0002A 46X, 113-114 cm, 198.70 meters composite depth, mcd). Morphologically closely related taxa, potentially re/presenting other species of Arcticacysta, have been previously recovered from the late Oligocene and early Miocene sediments of the Norwegian-Greenland Seas.

The View the MathML sourceTEX86H paleothermometer based on isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) has widely been applied in various marine settings to reconstruct past sea surface temperatures (SSTs). However, it still remains uncertain how well this proxy reconstructs annual mean SSTs. Here, we assess environmental factors governing the View the MathML sourceTEX86H paleothermometer in the Mediterranean Sea, by studying the distribution of isoGDGTs in surface sediments, suspended particulate matter (SPM), and two sediment cores. A redundancy analysis using the fractional abundance of the six major isoGDGTs indicates that the sedimentary isoGDGTs are mostly influenced by three environmental factors explaining a large part (74%) of the variance in isoGDGT distribution. In order of decreasing significance, these factors are annual mean SST, continental organic matter input as indicated by the BIT index, and water depth. However, when considering only the four isoGDGTs that are used for the View the MathML sourceTEX86H proxy, water depth is the most significant parameter, explaining 63% of the variance. Indeed, a strong positive relationship between water depth and View the MathML sourceTEX86H is observed in both surface sediments and SPM from the Mediterranean Sea. This is driven by an increase in fractional abundances of GDGT-2 and crenarchaeol regio-isomer and a decrease in the fractional abundances of GDGT-1 and GDGT-3 with increasing water depth, leading to a bias to higher temperatures of View the MathML sourceTEX86H in deep-water surface sediments. The fact that the water-depth trend is also apparent in SPM suggests that this change might be due to a change in thaumarchaeotal community thriving below surface mixed-layer waters and that this signal is, at least partly, incorporated into sedimentary isoGDGTs. Interestingly, surface-sediment View the MathML sourceTEX86H values from >1000 m water depth do not show a correlation with water depth anymore and instead are correlated to annual mean SSTs. A composite deep-water View the MathML sourceTEX86H dataset of surface sediments from both the Mediterranean Sea and the Red Sea, interconnected regional restricted basins with relatively high bottom-water temperatures and high salinity, forms a distinctive correlation line, statistically distinct from that of the general global correlation. Application of this correlation on two sedimentary records from the western Mediterranean Sea covering the last deglaciation yields SSTs nearly identical to those obtained with the View the MathML sourceU37K' paleothermometer, whereas the global calibration substantially overestimates SSTs. Our results show that the warm bias of the View the MathML sourceTEX86H proxy in the Mediterranean Sea is not due to seasonality, as previously suggested. Further research is needed to elucidate the mechanism behind the strong water depth trend of View the MathML sourceTEX86H in the Mediterranean Sea which is not apparent in open ocean settings.

Recent studies have correlated dinoflagellate resting cyst morphology to salinity and density variations in the water column, suggesting that morphology can be used for paleoceanographic reconstructions. However, the univariate statistics used by these studies are appropriate only where morphology is related to a single variable. Density is a function of salinity and temperature, so more advanced statistical methods are needed to understand which parameters affect morphology. In this study based on surface (coretop) sediments, a set of environmental variables (sea-surface salinity, temperature, nitrate, and phosphate) was simultaneously correlated to morphological variations seen in resting cysts produced by the dinoflagellate Protoceratium reticulatum (= Operculodinium centrocarpum sensu Wall and Dale). Approximately 3200 measurements were obtained from the North Atlantic Ocean and used to generate a working model based on the Akaike information criterion. Hierarchical partitioning was then applied to establish the independent and joint effects for each predictor variable. Results from these analyses showed that while salinity constitutes the dominant variable affecting process length in the cysts of P. reticulatum in the North Atlantic, it is not the sole explanatory variable and that multicollinearity exists. Temperature and nutrients also showed a significant relationship to the morphology, requiring multiple regression to construct a representative model. The applicability of the North Atlantic working model was finally evaluated by comparing the results to data from the Mediterranean, Marmara, and Black seas, and Baltic–Kattegat–Skagerrak estuarine system. This comparison showed regional differences in morphological–environmental correlation. While salinity constitutes the most important explanatory factor in both the North Atlantic and Baltic–Skagerrak system, this is not so for the Mediterranean–Black Sea region where temperature is the dominant variable. It is concluded that a predictive salinity model based on P. reticulatum cyst morphology has at best a regional application.

Recent studies have correlated dinoflagellate resting cyst morphology to salinity and density variations in the water column, suggesting that morphology can be used for paleoceanographic reconstructions. However, the univariate statistics used by these studies are appropriate only where morphology is related to a single variable. Density is a function of salinity and temperature, so more advanced statistical methods are needed to understand which parameters affect morphology. In this study based on surface (coretop) sediments, a set of environmental variables (sea-surface salinity, temperature, nitrate, and phosphate) was simultaneously correlated to morphological variations seen in resting cysts produced by the dinoflagellate Protoceratium reticulatum (=Operculodinium centrocarpum sensu Wall and Dale). Approximately 3200 measurements were obtained from the North Atlantic Ocean and used to generate a working model based on the Akaike information criterion. Hierarchical partitioning was then applied to establish the independent and joint effects for each predictor variable. Results from these analyses showed that while salinity constitutes the dominant variable affecting process length in the cysts of P. reticulatum in the North Atlantic, it is not the sole explanatory variable and that multicollinearity exists. Temperature and nutrients also showed a significant relationship to the morphology, requiring multiple regression to construct a representative model. The applicability of the North Atlantic working model was finally evaluated by comparing the results to data from the Mediterranean, Marmara, and Black seas, and Baltic-Kattegat-Skagerrak estuarine system. This comparison showed regional differences in morphological-environmental correlation. While salinity constitutes the most important explanatory factor in both the North Atlantic and Baltic-Skagerrak system, this is not so for the Mediterranean-Black Sea region where temperature is the dominant variable. It is concluded that a predictive salinity model based on P. reticulatum cyst morphology has at best a regional application.

Warm intervals within the Pliocene epoch (5.33–2.58 million years ago) were characterized by global temperatures comparable to those predicted for the end of this century1 and atmospheric CO2 concentrations similar to today2, 3, 4. Estimates for global sea level highstands during these times5 imply possible retreat of the East Antarctic ice sheet, but ice-proximal evidence from the Antarctic margin is scarce. Here we present new data from Pliocene marine sediments recovered offshore of Adélie Land, East Antarctica, that reveal dynamic behaviour of the East Antarctic ice sheet in the vicinity of the low-lying Wilkes Subglacial Basin during times of past climatic warmth. Sedimentary sequences deposited between 5.3 and 3.3 million years ago indicate increases in Southern Ocean surface water productivity, associated with elevated circum-Antarctic temperatures. The geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene.

Dinoflagellate cysts are useful for reconstructing upper water conditions. For adequate reconstructions detailed information is required about the relationship between modern day environmental conditions and the geographic distribution of cysts in sediments. This Atlas summarises the modern global distribution of 71 organic-walled dinoflagellate cyst species. The synthesis is based on the integration of literature sources together with data of 2405 globally distributed surface sediment samples that have been prepared with a comparable methodology and taxonomy. The distribution patterns of individual cyst species are being compared with environmental factors that are known to influence dinoflagellate growth, gamete production, encystment, excystment and preservation of their organic-walled cysts: surface water temperature, salinity, nitrate, phosphate, chlorophyll-a concentrations and bottom water oxygen concentrations. Graphs are provided for every species depicting the relationship between seasonal and annual variations of these parameters and the relative abundance of the species. Results have been compared with previously published records; an overview of the ecological significance as well as information about the seasonal production of each individual species is presented.The relationship between the cyst distribution and variation in the aforementioned environmental parameters was analysed by performing a canonical correspondence analysis. All tested variables showed a positive relationship on the 99% confidence level. Sea-surface temperature represents the parameter corresponding to the largest amount of variance within the dataset (40%) followed by nitrate, salinity, phosphate and bottom-water oxygen concentration, which correspond to 34%, 33%, 25% and 24% of the variance, respectively. Characterisations of selected environments as well as a discussion about how these factors could have influenced the final cyst yield in sediments are included.

Warm intervals within the Pliocene epoch (5.33-2.58 million years ago) were characterized by global temperatures comparable to those predicted for the end of this century and atmospheric CO 2 concentrations similar to today. Estimates for global sea level highstands during these times imply possible retreat of the East Antarctic ice sheet, but ice-proximal evidence from the Antarctic margin is scarce. Here we present new data from Pliocene marine sediments recovered offshore of Adélie Land, East Antarctica, that reveal dynamic behaviour of the East Antarctic ice sheet in the vicinity of the low-lying Wilkes Subglacial Basin during times of past climatic warmth. Sedimentary sequences deposited between 5.3 and 3.3 million years ago indicate increases in Southern Ocean surface water productivity, associated with elevated circum-Antarctic temperatures. The geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene. © 2013 Macmillan Publishers Limited. All rights reserved.

The Integrated Ocean Drilling Program Expedition 318 to the Wilkes Land margin of Antarctica recovered a sedimentary succession ranging in age from lower Eocene to the Holocene. Excellent stratigraphic control is key to understanding the timing of paleoceanographic events through critical climate intervals. Drill sites recovered the lower and middle Eocene, nearly the entire Oligocene, the Miocene from about 17 Ma, the entire Pliocene and much of the Pleistocene. The paleomagnetic properties are generally suitable for magnetostratigraphic interpretation, with well-behaved demagnetization diagrams, uniform distribution of declinations, and a clear separation into two inclination modes. Although the sequences were discontinuously recovered with many gaps due to coring, and there are hiatuses from sedimentary and tectonic processes, the magnetostratigraphic patterns are in general readily interpretable. Our interpretations are integrated with the diatom, radiolarian, calcareous nannofossils and dinoflagellate cyst (dinocyst) biostratigraphy. The magnetostratigraphy significantly improves the resolution of the chronostratigraphy, particularly in intervals with poor biostratigraphic control. However, Southern Ocean records with reliable magnetostratigraphies are notably scarce, and the data reported here provide an opportunity for improved calibration of the biostratigraphic records. In particular, we provide a rare magnetostratigraphic calibration for dinocyst biostratigraphy in the Paleogene and a substantially improved diatom calibration for the Pliocene. This paper presents the stratigraphic framework for future paleoceanographic proxy records which are being developed for the Wilkes Land margin cores. It further provides tight constraints on the duration of regional hiatuses inferred from seismic surveys of the region.

IODP Expedition 318 drilled several sites on the Wilkes Land margin of East Antarctica in Jan.–Feb. 2010. The principle objective of the cruise was to obtain a better understanding of the Cenozoic cryospheric evolution of Antarctica, in conjunction with the dating of major regional seismic unconformities WL-U3 thru U8. Unconformity WL-U3 was suggested to be related to the inception of Antarctic glaciation during the Eocene-Oligocene Transition (~34 Ma). Changes in biotic assemblages distinctly denote an ecological transition from warm, Eocene ice-free ‘greenhouse’ conditions to colder, highly productive, Oligocene ‘icehouse’ conditions, more akin to the modern shelf environment of Antarctica. Preliminary dinoflagellate, and TEX86 results will be discussed. In addition, our paleoecological interpretations provide constraints for on-going geophysical studies aimed at modelling changes in relative sea level in response to East Antarctic glaciation and ice-sheet arrival at the Wilkes Land margin

The high abundances and cyclic distribution of remains of the freshwater fern Azolla in early-Middle Eocene sediments from the Arctic Ocean have previously been related to episodic surface-water freshening, which was speculated to be orbitally modulated. Our integrated palynological and cyclostratigraphical analysis of the recovered Azolla interval in Integrated Ocean Drilling Program (IODP) core 302-M0004A-11X resulted in the recognition of two clear periodicities: a dominant ~1.2 m cyclicity, which we relate to changes in obliquity (~40 k.y.), and a weaker ~0.7 m cyclicity, which we link to precession (~21 k.y.). Cycles in the abundances of Azolla, cysts of freshwater-tolerant dinoflagellates, and swamp-vegetation pollen show covariability in the obliquity domain. This strong correlation suggests periods of enhanced rainfall and runoff during Azolla blooms, presumably linked to increased local summer temperatures during obliquity maxima. Larix and bisaccate conifer pollen covary at the precession frequency, with peak occurrences corresponding to precession minima, possibly as a result of enhanced continental runoff from a more remote source area and a stronger seasonal contrast. Following the sudden demise of Azolla ca. 48.1 Ma, runoff (cycles) continued to influence the central Arctic at decreased intensity. This and a concomitant decline in swamp-vegetation pollen suggest edaphically drier conditions on land and decreased runoff into the Arctic Ocean, causing salinity changes, which might have been fatal for Azolla. Moreover, a sea-level rise, inferred from overall decreasing total terrestrial palynomorph concentrations, possibly facilitated oceanic connections. © 2011 Geological Society of America.

Several episodes of abrupt and transient warming, each lasting between 50,000 and 200,000 years, punctuated the long-term warming during the Late Palaeocene and Early Eocene (58 to 51 Myr ago) epochs1,2. These hyperthermal events, such as the Eocene Thermal Maximum 2 (EMT2) that took place about 53.5 Myr ago2, are associated with rapid increases in atmospheric CO2 content. However, the impacts of most events are documented only locally86. Here we show, on the basis of estimates from the TEX 86 ′ proxy, that sea surface temperatures rose by 3-5 C in the Arctic Ocean during the EMT2. Dinoflagellate fossils demonstrate a concomitant freshening and eutrophication of surface waters, which resulted in euxinia in the photic zone. The presence of palm pollen implies5 that coldest month mean temperatures over the Arctic land masses were no less than 8 C, in contradiction of model simulations that suggest hyperthermal winter temperatures were below freezing6. In light of our reconstructed temperature and hydrologic trends, we conclude that the temperature and hydrographic responses to abruptly increased atmospheric CO2 concentrations were similar for the ETM2 and the better-described Palaeocene-Eocene Thermal Maximum7,8, 55.5 Myr ago. © 2009 Macmillan Publishers Limited. All rights reserved.

Absolute abundances (concentrations) of dinoflagellate cysts are often determined through the addition of Lycopodium clavatum marker-grains as a spike to a sample before palynological processing. An inter-laboratory calibration exercise was set up in order to test the comparability of results obtained in different laboratories, each using its own preparation method. Each of the 23 laboratories received the same amount of homogenized splits of four Quaternary sediment samples. The samples originate from different localities and consisted of a variety of lithologies. Dinoflagellate cysts were extracted and counted, and relative and absolute abundances were calculated. The relative abundances proved to be fairly reproducible, notwithstanding a need for taxonomic calibration. By contrast, excessive loss of Lycopodium spores during sample preparation resulted in non-reproducibility of absolute abundances. Use of oxidation, KOH, warm acids, acetolysis, mesh sizes larger than 15 µm and long ultrasonication (> 1 min) must be avoided to determine reproducible absolute abundances. The results of this work therefore indicate that the dinoflagellate cyst worker should make a choice between using the proposed standard method which circumvents critical steps, adding Lycopodium tablets at the end of the preparation and using an alternative method.

A biometrical analysis of the dinoflagellate cyst Lingulodinium machaerophorum [Deflandre, G., Cookson, I.C., 1955. Fossil microplankton from Australia late Mesozoic and Tertiary sediments. Australian journal of Marine and Freshwater Research 6: 242–313.] Wall, 1967 in 144 globally distributed surface sediment samples revealed that the average process length is related to summer salinity and temperature at a water depth of 30 m by the equation (salinity/temperature) = (0.078⁎average process length + 0.534) with R2 = 0.69. This relationship can be used to reconstruct palaeosalinities, albeit with caution. The particular ecological window can be associated with known distributions of the corresponding motile stage Lingulodinium polyedrum (Stein) Dodge, 1989. Confocal laser microscopy showed that the average process length is positively related to the average distance between process bases (R2 = 0.78), and negatively related to the number of processes (R2 = 0.65). These results document the existence of two end members in cyst formation: one with many short, densely distributed processes and one with a few, long, widely spaced processes, which can be respectively related to low and high salinity/temperature ratios. Obstruction during formation of the cysts causes anomalous distributions of the processes. From a biological perspective, processes function to facilitate sinking of the cysts through clustering.

Several episodes of abrupt and transient warming, each lasting between 50,000 and 200,000 years, punctuated the long-term warming during the Late Palaeocene and Early Eocene (58 to 51 Myr ago) epochs1,2. These hyperthermal events, such as the Eocene Thermal Maximum 2 (EMT2) that took place about 53.5 Myr ago2, are associated with rapid increases in atmospheric CO2 content. However, the impacts of most events are documented only locally86. Here we show, on the basis of estimates from the TEX 86 ′ proxy, that sea surface temperatures rose by 3-5 C in the Arctic Ocean during the EMT2. Dinoflagellate fossils demonstrate a concomitant freshening and eutrophication of surface waters, which resulted in euxinia in the photic zone. The presence of palm pollen implies5 that coldest month mean temperatures over the Arctic land masses were no less than 8 C, in contradiction of model simulations that suggest hyperthermal winter temperatures were below freezing6. In light of our reconstructed temperature and hydrologic trends, we conclude that the temperature and hydrographic responses to abruptly increased atmospheric CO2 concentrations were similar for the ETM2 and the better-described Palaeocene-Eocene Thermal Maximum7,8, 55.5 Myr ago. © 2009 Macmillan Publishers Limited. All rights reserved.

Drilling results from the Integrated Ocean Drilling Program’s Arctic Coring Expedition (ACEX) to the\ud Lomonosov Ridge (LR) document a 26 million year hiatus that separates freshwater-influenced biosilica-rich\ud deposits of the middle Eocene from fossil-poor glaciomarine silty clays of the early Miocene. Detailed\ud micropaleontological and sedimentological data from sediments surrounding this mid-Cenozoic hiatus describe\ud a shallow water setting for the LR, a finding that conflicts with predrilling seismic predictions and an initial\ud postcruise assessment of its subsidence history that assumed smooth thermally controlled subsidence following\ud rifting. A review of Cenozoic tectonic processes affecting the geodynamic evolution of the central Arctic Ocean\ud highlights a prolonged phase of basin-wide compression that ended in the early Miocene. The coincidence in\ud timing between the end of compression and the start of rapid early Miocene subsidence provides a compelling\ud link between these observations and similarly accounts for the shallow water setting that persisted more than\ud 30 million years after rifting ended. However, for much of the late Paleogene and early Neogene, tectonic\ud reconstructions of the Arctic Ocean describe a landlocked basin, adding additional uncertainty to reconstructions\ud of paleodepth estimates as the magnitude of regional sea level variations remains unknown.

The Cenozoic record of the Lomonosov Ridge (central Arctic Ocean) recovered during Integrated Ocean\ud Drilling Program (IODP) Expedition 302 revealed an unexpected 26 Ma hiatus, separating middle Eocene\ud (�44.4 Ma) from lower Miocene sediments (�18.2 Ma). To elucidate the nature of this unconformity, we\ud performed a multiproxy palynological (dinoflagellate cysts, pollen, and spores), micropaleontological\ud (siliceous microfossils), inorganic, and organic (Tetra Ether Index of lipids with 86 carbon atoms (TEX86)\ud and Branched and Isoprenoid Tetraether (BIT)) geochemical analysis of the sediments from �5 m below to\ud �7 m above the hiatus. Four main paleoenvironmental phases (A–D) are recognized in the sediments\ud encompassing the unconformity, two below (A–B) and two above (C–D): (A) Below the hiatus, proxies show\ud relatively warm temperatures, with Sea Surface Temperatures (TEX86-derived SSTs) of about 8�C and high\ud fresh to brackish water influence. (B) Approaching the hiatus, proxies indicate a cooling trend (TEX86-derived\ud SSTs of �5�C), increased freshwater influence, and progressive shoaling of the Lomonosov Ridge drilling\ud site, located close to or at sea level. (C) The interval directly above the unconformity contains sparse reworked\ud Cretaceous to Oligocene dinoflagellate cysts. Sediments were deposited in a relatively shallow, restricted\ud marine environment. Proxies show the simultaneous influence of both fresh and marine waters, with\ud alternating oxic and anoxic conditions. Pollen indicates a relatively cold climate. Intriguingly, TEX86-derived\ud SSTs are unexpectedly high, �15–19�C. Such warm surface waters may be partially explained by the\ud ingression of warmer North Atlantic waters after the opening of the Fram Strait during the early Miocene. (D)\ud Sediments of the uppermost interval indicate a phase of extreme oxic conditions, and a well-ventilated\ud environment, which occurred after the complete opening of the Fram Strait. Importantly, and in contrast with\ud classical postrifting thermal subsidence models for passive margins, our data suggest that sediment erosion\ud and/or nondeposition that generated the hiatus was likely due to a progressive shoaling of the Lomonosov\ud Ridge. A shallow water setting both before and after the hiatus suggests that the Lomonosov Ridge remained\ud at or near sea level for the duration of the gap in the sedimentary record. Interacting sea level changes and/or\ud tectonic activity (possibly uplift) must be invoked as possible causes for such a long hiatus.

We reconstruct the latest Paleocene and early Eocene (∼57-50 Ma) environmental trends in the Arctic Ocean and focus on the Paleocene-Eocene thermal maximum (PETM) (∼55 Ma), using strata recovered from the Lomonosov Ridge by the Integrated Ocean Drilling Program Expedition 302. The Lomonosov Ridge was still partially subaerial during the latest Paleocene and earliest Eocene and gradually subsided during the early Eocene. Organic dinoflagellate cyst (dinocyst) assemblages point to brackish and productive surface waters throughout the latest Paleocene and early Eocene. Dinocyst assemblages are cosmopolitan during this time interval, suggesting warm conditions, which is corroborated by TEX86′-reconstructed temperatures of 15°-18°C. Inorganic geochemistry generally reflects reducing conditions within the sediment and euxinic conditions during the upper lower Eocene. Spectral analysis reveals that the cyclicity, recorded in X-ray fluorescence scanning Fe data from close to Eocene thermal maximum 2 (∼53 Ma, presence confirmed by dinocyst stratigraphy), is related to precession. Within the lower part of the PETM, proxy records indicate enhanced weathering, runoff, anoxia, and productivity along with sea level rise. On the basis of total organic carbon content and variations in sediment accumulation rates, excess organic carbon burial in the Arctic Ocean appears to have contributed significantly to the sequestration of injected carbon during the PETM.

This Explanatory Notes section complements and supports four other documents, which collectively describe the process and procedures of scientific investigations employed during the ANDRILL SMS Project: (1) ANDRILL Southern McMurdo Sound Project - Scientific Prospectus (ANDRILL contribution 5 - Harwood et al., 2005); (2) a Science Plan summary of SMS Project research compiled from research proposals of Science Team menbers (available on the SMS Project ‘Science Drive’ – Harwood et al., 2007); (3) SMS Project Science Logistics Implementation Plan (SLIP) - draft documents developed and distributed to SMS team members prior to deployment; (4) Operations overview – Falconer et al., this volume). These five documents, and information presented (also available on the SMS Project ‘Science Drive’) at McMurdo Station during the initial morning meetings by co-chief scientists, staff scientist, media coordinator, curator and discipline team leaders, represent the essential elements of the full Science Logistics Implementation Plan (SLIP) for the SMS Project. Please also refer to the McMurdo Ice Shelf Project SLIP available at www.andrill.org (ANDRILL contribution 7 – Naish et al., 2005) for additional background information related to SMS science logistics and operations. These explanatory notes provide important background information on the nature of data present on the SMS Project ‘Science Drive’, including the on-ice report, other core characterization data, and documents and data that record the activities of the SMS Project Science Team.

We reconstruct the latest Paleocene and early Eocene (∼57-50 Ma) environmental trends in the Arctic Ocean and focus on the Paleocene-Eocene thermal maximum (PETM) (∼55 Ma), using strata recovered from the Lomonosov Ridge by the Integrated Ocean Drilling Program Expedition 302. The Lomonosov Ridge was still partially subaerial during the latest Paleocene and earliest Eocene and gradually subsided during the early Eocene. Organic dinoflagellate cyst (dinocyst) assemblages point to brackish and productive surface waters throughout the latest Paleocene and early Eocene. Dinocyst assemblages are cosmopolitan during this time interval, suggesting warm conditions, which is corroborated by TEX86′-reconstructed temperatures of 15°-18°C. Inorganic geochemistry generally reflects reducing conditions within the sediment and euxinic conditions during the upper lower Eocene. Spectral analysis reveals that the cyclicity, recorded in X-ray fluorescence scanning Fe data from close to Eocene thermal maximum 2 (∼53 Ma, presence confirmed by dinocyst stratigraphy), is related to precession. Within the lower part of the PETM, proxy records indicate enhanced weathering, runoff, anoxia, and productivity along with sea level rise. On the basis of total organic carbon content and variations in sediment accumulation rates, excess organic carbon burial in the Arctic Ocean appears to have contributed significantly to the sequestration of injected carbon during the PETM.

The coastal wetland ecosystems in Florida are highly sensitive to changes in freshwater budget, which is driven by regional sea surface temperature, tropical storm activity, and the El Niño-Southern Oscillation (ENSO). Although studying Florida wetlands is pivotal to the understanding of these interacting climate systems, wetland dynamics have been severely altered by recent land use and drainage activities. To gather insights into the natural variability of the coastal ecosystems in Florida versus the effects of anthropogenic impact in the area, we present a 300-year record of changes in the hydrological cycle from a shallow subtropical estuary (Rookery Bay) on the western shelf of Florida, Gulf of Mexico. Palynological (pollen and organic-walled dinoflagellate cysts), diatom, and sedimentological analyses of a sediment core reveal significant changes in past runoff and wetland development. The onset and development of human impact in Florida are evident from high influx of Ambrosia pollen at about A.D. 1900, indicative of land clearance and disturbed conditions. To date, this is the southernmost record of Ambrosia increase related to human impact in the United States. Wetland drainage and deforestation since A.D. 1900 are evident from the reduced freshwater wetland and pine vegetation, and lower abundances of phytoplankton species indicative of lagoonal and brackish conditions. High runoff after A.D. 1900 relates to increased erosionand may correspondingly reflect higher impact from hurricane landfalls in SW Florida. Several phases with high siliciclastic input and greater wetland pollen abundance occur that predate the human impact period. These phases are interpreted as periods with higher runoff and are likely related to regional longer-term climate variability. Copyright 2008 by the American Geophysical Union.

This Explanatory Notes section complements and supports four other documents, which collectively describe the process and procedures of scientific investigations employed during the ANDRILL SMS Project: (1) ANDRILL Southern McMurdo Sound Project - Scientific Prospectus (ANDRILL contribution 5 - Harwood et al., 2005); (2) a Science Plan summary of SMS Project research compiled from research proposals of Science Team menbers (available on the SMS Project ‘Science Drive’ – Harwood et al., 2007); (3) SMS Project Science Logistics Implementation Plan (SLIP) - draft documents developed and distributed to SMS team members prior to deployment; (4) Operations overview – Falconer et al., this volume). These five documents, and information presented (also available on the SMS Project ‘Science Drive’) at McMurdo Station during the initial morning meetings by co-chief scientists, staff scientist, media coordinator, curator and discipline team leaders, represent the essential elements of the full Science Logistics Implementation Plan (SLIP) for the SMS Project. Please also refer to the McMurdo Ice Shelf Project SLIP available at www.andrill.org (ANDRILL contribution 7 – Naish et al., 2005) for additional background information related to SMS science logistics and operations. These explanatory notes provide important background information on the nature of data present on the SMS Project ‘Science Drive’, including the on-ice report, other core characterization data, and documents and data that record the activities of the SMS Project Science Team.