The measurement of lipid phosphate is proposed as an indicator of microbial biomass in marine and estuarine sediments. This relatively simple assay can be performed on fresh, frozen or frozen-lyophilized sediment samples with chloroform methanol extraction and subsequent phosphate determination. The sedimentary lipid phosphate recovery correlates with the extractible ATP and the rate of DNA synthesis. Pulse-chase experiments show active metabolism of the sedimentary phospholipids. The recovery of added C-labeled bacterial lipids from sediments is quantitative. Replicate analyses from a single sediment sample gave a standard deviation of 11%. The lipid extract can be fractionated by relatively simple procedures and the plasmalogen, diacyl phospholipid, phosphonolipid and non-hydrolyzable phospholipid content determined. The relative fatty acid composition can be readily determined by gas-liquid chromatography.The lipid composition can be used to define the microbial community structure. For example, the absence of polyenoic fatty acids indicates minimal contamination with benthic micro-eukaryotes. Therefore the high content of plasmalogen phospholipids in these sediments suggests that the anaerobic prokaryotic Clostridia are found in the aerobic sedimentary horizon. This would require anaerobic microhabitats in the aerated zones.

The Last Glacial Maximum (LGM), one of the best-studied paleoclimatic intervals, o↵ers a prime opportunity to investigate how the climate system responds to changes in greenhouse gases (GHGs) and the cryosphere. Previous work has sought to constrain the magnitude and pattern of glacial cooling from paleothermometers, but the uneven distribution of the proxies, as well as their uncertainties, has challenged the construction of a full-field view of the LGM climate state. Here, we combine a large collection of geochemical proxies for sea-surface temperature with an isotope-enabled climate model ensemble to produce a field reconstruction of LGM temperatures using data assimilation. The reconstruction is validated with withheld proxies as well as independent ice core and speleothem 18 O measurements. Our assimilated product provides a precise constraint on global mean LGM cooling of 5.9 C (6.3-5.6 C, 95% CI). Given assumptions concerning the radiative forcing of GHGs, ice sheets, and aerosols, this cooling translates to an equilibrium climate sensitivity (ECS) of 3.2 C (2.2-4.3 C, 95% CI), a value that is higher than previous estimates and but consistent with the traditional consensus range of 2-4.5 C.

Climate changes across the last 24,000 years provide key insights into Earth system responses to external forcing. Climate model simulations 1, 2 and proxy data 3-8 have independently allowed for study of this crucial interval; however, they have at times yielded disparate conclusions. Here, we leverage both types of information using paleoclimate data assimilation 9, 10 to produce the first observationally constrained, full-field reanalysis of surface temperature change spanning the Last Glacial Maximum to present. We demonstrate that temperature variability across the last 24 kyr was linked to two modes: radiative forcing from ice sheets and greenhouse gases; and a superposition of changes in thermohaline circulation and seasonal insolation. In contrast with previous proxy-based reconstructions 6, 7 our reanalysis results show that global mean temperatures warmed between the early and middle Holocene and were stable thereafter. When compared with recent temperature changes 11 , our reanalysis indicates that both the rate and magnitude of modern observed warming are unprecedented relative to the changes of the last 24 kyr.

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The Last Glacial Maximum (LGM), one of the best-studied paleoclimatic intervals, offers a prime opportunity to investigate how the climate system responds to changes in greenhouse gases (GHGs) and the cryosphere. Previous work has sought to constrain the magnitude and pattern of glacial cooling from paleothermometers, but the uneven distribution of the proxies, as well as their uncertainties, has challenged the construction of a full-field view of the LGM climate state. Here, we combine a large collection of geochemical proxies for sea-surface temperature with an isotope-enabled climate model ensemble to produce a field reconstruction of LGM temperatures using data assimilation. The reconstruction is validated with withheld proxies as well as independent ice core and speleothem d18O measurements. Our assimilated product provides a precise constraint on global mean LGM cooling of -5.9˚C (-6.3 – -5.6˚C, 95% CI). Given assumptions concerning the radiative forcing of GHGs, ice sheets, and aerosols, this cooling translates to an equilibrium climate sensitivity (ECS) of 3.2˚C (2.2 – 4.3˚C, 95% CI), a value that is higher than previous estimates and but consistent with the traditional consensus range of 2 – 4.5˚C.

Sedimentologic and geochemical studies of box and gravity cores recovered from the Black Sea during the first leg of a multileg international Black Sea expedition in 1988 allow reconstruction of the basinwide Holocene environmental history of the Black Sea. In the deeper parts of the basin, box cores typically recovered a flocculent surface layer (“fluff”), laminated coccolith marls of Unit I (25–45 cm thick), and the upper 5–10 cm of finely laminated, dark‐colored sapropels of Unit II. Fine‐grained, homogeneous mud turbidites are interbedded with Units I and II over much of the basin, but the stratigraphie position of these turbidites differs, from site to site. The deposition of individual turbidites up to 15 cm thick does not appear to have significantly disturbed underlying laminae. Sediment trap deployments in the Black Sea suggest that light and dark laminae couplets represent annual increments of sedimentation (i.e., varves); we have therefore constructed a varve chronology for the sequence in order to correlate and date distinctive sedimentation and paleoenvironmental events. Distinctive groups of laminae in Unit I can be correlated across the entire deeper basin (a distance of more than 1000 km). This implies a remarkable homogeneity in production, accumulation, and preservation of biogenic material over much of the Black Sea during deposition of Unit I. The change from deposition of finely laminated, organic carbon‐rich sapropels (Unit II) to laminated, more calcareous, coccolith‐rich marls (Unit I) is thought to represent the crossing of a salinity threshold for Emiliania huxleyi. The varve chronology sets this change at about 1.63 ka (1633±100 yr B.P.), but the record of magnetic secular variation measured in several cores produces an age estimate of about 2.0 ka for the base of Unit I, or about 1.2 times the varve age. The average of six calibrated accelerator mass spectrometry radiocarbon ages for the base of Unit I is 2.7 ka, or about 1.7 times the varve age. Following the initial change to coccolith‐dominated sedimentation, deposition of sapropel resumed for at least one significant period, 1.56–1.25 ka. Since 1.25 ka, cycles of carbonate deposition with quasi‐decadal periodicities have produced characteristic darker and lighter assemblages of laminae. These cycles may have been climatically driven. Geochemical analyses coupled with the varve ages adopted herein indicate that accumulation rates of carbonate are nearly an order of magnitude higher in Unit I (averaging 35–45 g m−2 yr−1) than in sapropelic Unit II. which contains primarily detrital carbonate. The accumulation of lithogenic components in parts of Unit I is only 1.5 times the rate in Unit II. Deepwater organic carbon accumulation rates are somewhat higher in Unit I (3.5–4.5 g m−2 yr−1) than in the upper part of Unit II. Organic carbon accumulation rates in Unit I are somewhat antithetic to those of carbonate, and on the basis of this and additional constraints placed by pyrolysis and carbon isotopic analyses of organic material, it app...

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