A Late Pleistocene sea level stack

Late Pleistocene sea level has been reconstructed from ocean sediment core data using a wide variety of proxies and models. However, the accuracy of individual reconstructions is limited by measurement error, local variations in salinity and temperature, and assumptions particular to each technique. Here we present a sea level stack (average) which increases the signal-to-noise ratio of individual reconstructions. Specifically, we perform principal component analysis (PCA) on seven records from 0-430 ka and five records from 0-798 ka. The first principal component, which we use as the stack, describes ~80 % of the variance in the data and is similar using either five or seven records. After scaling the stack based on Holocene and Last Glacial Maximum (LGM) sea level estimates, the stack agrees to within 5 m with isostatically adjusted coral sea level estimates for Marine Isotope Stages 5e and 11 (125 and 400 ka, respectively). When we compare the sea level stack with the d18O of benthic foraminifera, we find that sea level change accounts for about ~40 % of the total orbital-band variance in benthic d18O, compared to a 65 % contribution during the LGM-to-Holocene transition. Additionally, the second and third principal components of our analyses reflect differences between proxy records associated with spatial variations in the d18O of seawater.

Sediment accretion and organic carbon burial relative to sea-level rise and storm events in two mangrove forests in Everglades National Park

The goal of this investigation was to examine how sediment accretion and organic carbon (OC) burial rates in mangrove forests respond to climate change. Specifically, will the accretion rates keep pace with sea-level rise, and what is the source and fate of OC in the system? Mass accumulation, accretion and OC burial rates were determined via 210Pb dating (i.e. 100 year time scale) on sediment cores collected from two mangrove forest sites within Everglades National Park, Florida (USA). Enhanced mass accumulation, accretion and OC burial rates were found in an upper layer that corresponded to a well-documented storm surge deposit. Accretion rates were 5.9 and 6.5 mm yr− 1 within the storm deposit compared to overall rates of 2.5 and 3.6 mm yr− 1. These rates were found to be matching or exceeding average sea-level rise reported for Key West, Florida. Organic carbon burial rates were 260 and 393 g m− 2 yr− 1 within the storm deposit compared to 151 and 168 g m− 2 yr− 1 overall burial rates. The overall rates are similar to global estimates for OC burial in marine wetlands. With tropical storms being a frequent occurrence in this region the resulting storm surge deposits are an important mechanism for maintaining both overall accretion and OC burial rates. Enhanced OC burial rates within the storm deposit could be due to an increase in productivity created from higher concentrations of phosphorus within storm-delivered sediments and/or from the deposition of allochthonous OC. Climate change-amplified storms and sea-level rise could damage mangrove forests, exposing previously buried OC to oxidation and contribute to increasing atmospheric CO2 concentrations. However, the processes described here provide a mechanism whereby oxidation of OC would be limited and the overall OC reservoir maintained within the mangrove forest sediments.

Sediment Accretion and Organic Carbon Burial Relative to Sea-Level Rise and Storm Events in Two Mangrove Forests in Everglades National Park

The goal of this investigation was to examine how sediment accretion and organic carbon (OC) burial rates in mangrove forests respond to climate change. Specifically, will the accretion rates keep pace with sea-level rise, and what is the source and fate of OC in the system? Mass accumulation, accretion and OC burial rates were determined via 210Pb dating (i.e. 100 year time scale) on sediment cores collected from two mangrove forest sites within Everglades National Park, Florida (USA). Enhanced mass accumulation, accretion and OC burial rates were found in an upper layer that corresponded to a well-documented storm surge deposit. Accretion rates were 5.9 and 6.5 mm yr− 1 within the storm deposit compared to overall rates of 2.5 and 3.6 mm yr− 1. These rates were found to be matching or exceeding average sea-level rise reported for Key West, Florida. Organic carbon burial rates were 260 and 393 g m− 2 yr− 1 within the storm deposit compared to 151 and 168 g m− 2 yr− 1 overall burial rates. The overall rates are similar to global estimates for OC burial in marine wetlands. With tropical storms being a frequent occurrence in this region the resulting storm surge deposits are an important mechanism for maintaining both overall accretion and OC burial rates. Enhanced OC burial rates within the storm deposit could be due to an increase in productivity created from higher concentrations of phosphorus within storm-delivered sediments and/or from the deposition of allochthonous OC. Climate change-amplified storms and sea-level rise could damage mangrove forests, exposing previously buried OC to oxidation and contribute to increasing atmospheric CO2 concentrations. However, the processes described here provide a mechanism whereby oxidation of OC would be limited and the overall OC reservoir maintained within the mangrove forest sediments.

Relative sea-level history of Marguerite Bay, Antarctic Peninsula derived from optically stimulated luminescence-dated beach cobbles

Calmette Bay within Marguerite Bay along the western side of the Antarctic Peninsula contains one of the most continuous flights of raised beaches described to date in Antarctica. Raised beaches extend to 40.8 m above sea level (masl) and are thought to reflect glacial isostatic adjustment due to the retreat of the Antarctic Peninsula Ice Sheet. Using optically stimulated luminescence (OSL), we dated quartz extracts from cobble surfaces buried in raised beaches at Calmette Bay. The beaches are separated into upper and lower beaches based on OSL ages, geomorphology, and sedimentary fabric. The two sets of beaches are separated by a prominent scarp. One of our OSL ages from the upper beaches dates to 9.3 thousand years ago (ka; as of 1950) consistent with previous extrapolation of sea-level data and the time of ice retreat from inner Marguerite Bay. However, four of the seven ages from the upper beaches date to the timing of glaciation. We interpret these ages to represent reworking of beaches deposited prior to the Last Glacial Maximum (LGM) by advancing and retreating LGM ice. Ages from the lower beaches record relative sea-level fall due to Holocene glacial-isostatic adjustment. We suggest a Holocene marine limit of 21.7 masl with an age of 5.5-7.3 ka based on OSL ages from Calmette Bay and other sea-level constraints in the area. A marine limit at 21.7 masl implies half as much relative sea-level change in Marguerite Bay during the Holocene as suggested by previous sea-level reconstructions. No evidence for a relative sea-level signature of neoglacial events, such as a decrease followed by an increase in RSL fall due to ice advance and retreat associated with the Little Ice Age, is found within Marguerite Bay indicating either: (1) no significant neoglacial advances occurred within Marguerite Bay; (2) rheological heterogeneity allows part of the Antarctic Peninsula (i.e. the South Shetland Islands) to respond to rapid ice mass changes while other regions are incapable of responding to short-lived ice advances; or (3) the magnitude of neoglacial events within Marguerite Bay is too small to resolve through relative sea-level reconstructions. Although the application of reconstructing sea-level histories using OSL-dated raised beach deposits provides a better understanding of the timing and nature of relative sea-level change in Marguerite Bay, we highlight possible problems associated with using raised beaches as sea-level indices due to post-depositional reworking by storm waves.

A 5 million year reconstruction of sea level, temperature, and sea water d18O

Marine sediment records from the Oligocene and Miocene reveal clear 400,000-year (400-kyr) climate cycles related to variations in orbital eccentricity. These cycles are also observed in the Plio-Pleistocene records of the global carbon cycle. However they are absent in the Late Pleistocene ice-age record over the past 1.5 million years. Here, we present a simulation of global ice volume over the past 5 million years with a coupled system of four 3-D ice-sheet models. Our simulation shows that the 400-kyr long eccentricity cycles of Antarctica vary coherently with d13C records during the Pleistocene suggesting that they drive the long-term carbon cycle changes throughout the past 35 million years. The 400-kyr response of Antarctica is eventually suppressed by the dominant 100-kyr glacial cycles of the large ice sheets in the Northern Hemisphere (NH).

Grain size distribution and sea level changes in Gåsfjärden fjord

We analysed long-term variations in grain-size distribution in sediments from Gåsfjärden, a fjord-like inlet on the south-west Baltic Sea, and explored potential drivers of the recorded changes in sediment grain-size data. Over the last 5.4 thousand years (ka), the relative sea level decreased 17 m in the study region, caused by isostatic land uplift. As a consequence, Gåsfjärden has been transformed from an open coastal setting into a semi-closed inlet surrounded on the east by numerous small islands. To quantitatively estimate the morphological changes in Gåsfjärden over the last 5.4 ka and to further link the changes to our grain-size data, a digital elevation model (DEM)-based openness index was calculated. In the period between 5.4 and 4.4 ka BP, the inlet was characterised by the largest openness index. During this interval, the highest sand contents (~0.4 %) and silt/clay ratios (~0. 3) in the sediment sequence were recorded, indicating relatively high bottom water energy. After 4.4 ka BP, the average sand content was halved to ~0.2 % and the silt/clay ratios showed a significant decreasing trend over the last 4 ka. These changes are found to be associated with the gradual embayment of Gåsfjärden as represented in the openness index. The silt/clay ratios exhibited a delayed and slower change compared with the sand contents, which further suggest that finer particles are less sensitive to changes in hydrodynamic energy. Our DEM-based coastal openness index has proved to be a useful tool for interpreting the sedimentary grain-size record.

Stable oxygen isotope data and geophysical measurements from Red Sea of core M174/Kl11

To settle debate on the timing of sea level fluctuations during marine isotope stage (MIS) 3, we present records of d18O ruber (sea level proxy) and magnetic susceptibility from the same samples within the single sediment archive (i.e., "coregistered") of central Red Sea core GeoTü-KL11. Core-scanning X-ray fluorescence and environmental magnetic data establish the suitability of magnetic susceptibility as a proxy for eolian dust content in Red Sea sediments. The eolian dust data record similar variability as Greenland d18O ice during early to middle MIS 3, in agreement with previous observations that regional Arabian Sea climate fluctuated with a timing similar to that of Greenland climate variations. In contrast, the sea level record fluctuates with a timing similar to that of Antarctic-style climate variations. The coregistered nature of the two records in core KL11 unambiguously reveals a distinct offset in the phase relationship between sea level and eolian dust fluctuations. The results confirm that sea level rises, indicated by shifts in Red Sea d18O ruber to lighter values, occurred during cold episodes in Greenland during early to middle MIS 3. This indicates that the amplitudes of the reconstructed MIS 3 sea level fluctuations would not be reduced by inclusion of regional climate fluctuations in the Red Sea sea level method. Our analysis comprehensively supports our earlier conclusions of large-amplitude sea level variations during MIS 3 with a timing that is strongly similar to Antarctic-style climate variations.

Sea-level control on the connection between shelf-edge deltas and the Bourcart canyon head (western Mediterranean) during the last glacial/interglacial cycle

A dense grid of high- and very high resolution seismic data, together with piston cores and borehole data providing time constraints, enables us to reconstruct the history of the Bourcart canyon head in the western Mediterranean Sea during the last glacial/interglacial cycle. The canyon fill is composed of confined channel–levee systems fed by a series of successively active shelf fluvial systems, originating from the west and north. Most of the preserved infill corresponds to the interval between Marine Isotope Stage (MIS) 3 and the early deglacial (19 cal ka BP). Its deposition was strongly controlled by a relative sea level that impacted the direct fluvial/canyon connection. During a period of around 100 kyr between MIS 6 and MIS 2, the canyon “prograded” by about 3 km. More precisely, several parasequences can be identified within the canyon fill. They correspond to forced-regressed parasequences (linked to punctuated sea-level falls) topped by a progradational-aggradational parasequence (linked to a hypothetical 19-ka meltwater pulse (MWP)). The bounding surfaces between forced-regressed parasequences are condensed intervals formed during intervals of relative sediment starvation due to flooding episodes. The meandering pattern of the axial incision visible within the canyon head, which can be traced landward up to the Agly paleo-river, is interpreted as the result of hyperpycnal flows initiated in the river mouth in a context of increased rainfall and mountain glacier flushing during the early deglacial.