Hypoxia in the Holocene Baltic Sea : Comparing modern versus past intervals using sedimentary trace metals

Anthropogenic nutrient input has caused a rapid expansion of bottom water hypoxia in the Baltic Sea over the past century. Two earlier intervals of widespread hypoxia, coinciding with the Holocene Thermal Maximum (HTMHI; 8-4 ka before present; BP) and the Medieval Climate Anomaly (MCA(HI); similar to 1200-750 years BP), have been identified from Baltic Sea sediments. Here we present sediment records from two sites in the Baltic Sea, and compare the trace metal (As, Ba, Cd, Cu, Mo, Ni, Pb, Re, Sb, Tl, U, V, Zn) enrichments during all three hypoxic intervals. Distinct differences are observed between the intervals and the various elements, highlighting the much stronger perturbation of trace metal cycles during the modern hypoxic interval. Both Mo and U show a strong correlation with C-org and very high absolute concentrations, indicative of frequently euxinic bottom waters during hypoxic intervals. During the modern hypoxic interval (Modern(HI)) comparatively less Mo is sequestered relative to C-org than in earlier intervals. This suggests partial drawdown of the water column Mo inventory in the modern water column due to persistent euxinia and only partial replenishment of Mo through North Sea inflows. Molybdenum contents in modern sediments are likely also affected by the recent slowdown in input of Mo in association with deposition of Fe and Mn oxides. Strong enrichments of U in recent sediments confirm that the Modern(HI) is more intense than past intervals. These results suggest that U is a more reliable indicator for the intensity of bottom water deoxygenation in the Baltic Sea than Mo. Sedimentary Re enrichment commences under mildly reducing conditions, but this element is not further enriched under more reducing conditions. Enrichments of V are relatively minor for the MCA(HI) and Modern(HI), possibly due to strong reservoir effects on V in the water column, indicating that V is unreliable as an indicator for the intensity of bottom water hypoxia in this setting. Furthermore, Ba profiles are strongly influenced by post-depositional remobilization throughout the Holocene. The strong relationship between C-org and Ni, Tl and particularly Cu suggests that these trace metals can be used to reconstruct the C-org flux into the sediments. Profiles of As, Sb and Cd and especially Pb and Zn are strongly influenced by anthropogenic pollution.Peer reviewe

A key role for iron-bound phosphorus in authigenic apatite formation in North Atlantic continental platform sediments

A combination of pore water and solid phase analysis was used to determine whether authigenic carbonate fluorapatite (CFA) is currently forming in the sediment at two locations (OMEX I and II) on the North Atlantic continental platform Goban Spur (southwest of Ireland). Results of selective P extractions suggest that an early diagenetic redistribution of Fe-bound P to an authigenic P phase may be occurring at both stations. A steady-state diagenetic model describing the depth profiles of pore water HPO42− and three solid phase forms of P (organic P, Fe-bound P and authigenic P) was developed and applied to the data of station OMEX-I. The model results indicate that CFA formation can account for the observed increase of authigenic P with depth at this station. Furthermore, the results show that an intense cycling of P between Fe-bound P and pore water HPO42− at the redox interface can create conditions beneficial for CFA formation. This internal P cycle is driven by downward, bioturbational transport of mainly in-situ-formed Fe-bound P into the reduced sediment zone. Losses from the internal P cycle due to CFA formation and HPO42− diffusion are compensated for by sorption of HPO42− released from organic matter to Fe oxides in the oxidized surface sediment. Fe-bound P thus acts as an intermediate between organic P and CFA. CFA can account for between 25 and 70% of the total burial flux of reactive P at station OMEX-I and thus may act as an important sink for P in this low sedimentation, continental margin environment

Із зали засідань Президії НАН України (24 жовт­ня 2012 року)

На черговому засіданні Президії НАН України 24 жовтня 2012 року члени Президії НАН України та запрошені заслухали такі питання: про діяльність Державного агентства з питань науки, інновацій та інформатизації України з удосконалення нормативно-правової бази у сфері наукової, науково-технічної, інноваційної діяльності та інформатизації протягом 2011–2012 рр. (доповідач — голова Агентства академік НАН України В.П. Семиноженко); про наукову та науково-організаційну діяльність Інституту хімії високомолекулярних сполук НАН України (доповідач — академік НАН України Є.В. Лебедєв); сучасні уявлення про механізми тертя (доповідач — доктор фізико-математичних наук О.М. Браун); про нагородження відзнаками НАН України та Почесними грамотами НАН України і Центрального комітету профспілки працівників НАН України (доповідач — академік НАН України В.Ф. Мачулін); кадрові та поточні питання

pH-Dependent iron oxide precipitation in a subterranean estuary

Author Posting. © The Authors, 2005. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Geochemical Exploration 88 (2006): 399-403, doi:10.1016/j.gexplo.2005.08.084.Iron-oxide coated sediment particles in subterranean estuaries can act as a geochemical barrier (“iron curtain”) for various chemical species in groundwater (e.g. phosphate), thus limiting their discharge to coastal waters. Little is known about the factors controlling this Fe-oxide precipitation. Here, we implement a simple reaction network in a 1D reactive transport model (RTM), to investigate the effect of O2 and pH gradients along a flow-line in the subterranean estuary of Waquoit Bay (Cape Cod, Massachusetts) on oxidative precipitation of Fe(II) and subsequent PO4 sorption. Results show that the observed O2 gradient is not the main factor controlling precipitation and that it is the pH gradient at the mixing zone of freshwater (pH 5.5) and seawater (pH 7.9) near the beach face that causes a ~7-fold increase in the rate of oxidative precipitation of Fe(II) at ~15 m. Thus, the pH gradient determines the location and magnitude of the observed iron oxide accumulation and the subsequent removal of PO4 in this subterranean estuary.Financial support was provided by the Netherlands Organisation for Scientific Research (NWO) and WHOI Guest Student Program (grants to C. Spiteri), the Royal Netherlands Academy of Arts and Sciences (KNAW) (fellowship to C.P. Slomp) and US National Science Foundation NSF-OCE0095384 and NSF-OCE0425061 (grants to M.A. Charette)

Molybdenum dynamics in sediments of a seasonally-hypoxic coastal marine basin

Peer reviewe

Rheological and Microstructural Changes of Oat and Barley Starches During Heating and Cooling

Microstructural and rheological changes in barley and oat starch dispersions during heating and cooling were studied by light microscopy and dynamic viscoelastic measurements. The two starch pastes showed similar viscoelastic properties after gelatinization, but during cooling the 20% barley starch pastes heated at 95°C underwent a sharp transition in viscoelastic behaviour probably due to the gelation of amylose. This transition was shifted to lower temperatures at 10% starch concentration. Microstructural studies of an 8% barley starch dispersion heated to 90°C using the smear technique showed amylose to form a network structure around the granules. The granules in starch paste heated to 95°C were poorly stained and amylopectin was fragmented. Microscopic examination of an embedded section of the cooled barley starch gel showed amylose to form a continuous phase in which starch granules were dispersed. G\u27 increased below 80°C during cooling of 10% oat starch dispersions preheated at 95 °C. No rheological changes occurred when they were preheated at only 90°C. Microstructural studies of an 8% oat starch dispersion heated to 90°C using the smear technique showed amylose to form a network structure around the granules. Part of the granule structure had already broken down. Heating to 95°C induced considerable changes in the granule structure of oat starch gels. Amylopectin formed a very fine network. Microscopic examination of embedded sections of the cooled, stored gel showed a much coarser structure compared with that of the smear

Recovery from multi‐millennial natural coastal hypoxia in the Stockholm Archipelago, Baltic Sea, terminated by modern human activity

Enhanced nutrient input and warming have led to the development of low oxygen (hypoxia) in coastal waters globally. For many coastal areas, insight into redox conditions prior to human impact is lacking. Here, we reconstructed bottom water redox conditions and sea surface temperatures (SSTs) for the coastal Stockholm Archipelago over the past 3000 yr. Elevated sedimentary concentrations of molybdenum indicate (seasonal) hypoxia between 1000b.c.e.and 1500c.e. Biomarker-based (TEX86) SST reconstructions indicate that the recovery from hypoxia after 1500c.e.coincided with a period of significant cooling (similar to 2 degrees C), while human activity in the study area, deduced from trends in sedimentary lead and existing paleobotanical and archeological records, had significantly increased. A strong increase in sedimentary lead and zinc, related to more intense human activity in the 18(th)and 19(th)century, and the onset of modern warming precede the return of hypoxia in the Stockholm Archipelago. We conclude that climatic cooling played an important role in the recovery from natural hypoxia after 1500c.e., but that eutrophication and warming, related to modern human activity, led to the return of hypoxia in the 20(th)century. Our findings imply that ongoing global warming may exacerbate hypoxia in the coastal zone of the Baltic Sea

Isotopic characterization of methane: insights from clumped isotope (13CDH3 and CD2H2) measurements

Atmospheric methane is an important greenhouse gas, and various methods are used to identify and quantify its sources. The measurement of bulk isotopic composition (δ13C and δD) is a widely used characterization technique, but due to the overlap of source signatures, it is often difficult to distinguish between thermogenic, microbial, and other sources. With the advancement of high-resolution mass spectrometry, it is now possible to measure the rare clumped isotopologues of methane 13CDH3 and CD2H2. This novel method can give additional information to help constrain methane sources and processes. The clumping anomaly is temperature-dependent and can thus be used to calculate the formation or equilibration temperature when methane is in thermodynamic equilibrium. In case of thermodynamic disequilibrium, the clumped signatures can be exploited to identify various kinetic gas formation and fractionation (mixing, diffusion, etc.) processes. We have developed a technique to extract pure methane from air and water samples and to measure the clumped isotope signatures (Δ13CDH3 and ΔCD2H2) with high precision and reproducibility, using the Thermo Ultra mass spectrometer. We will present the current capabilities of this setup, and the results of the first sets of samples measured from different natural environments

Iron-Phosphorus Feedbacks Drive Multidecadal Oscillations in Baltic Sea Hypoxia

Hypoxia has occurred intermittently in the Baltic Sea since the establishment of brackish-water conditions at similar to 8,000 years B.P., principally as recurrent hypoxic events during the Holocene Thermal Maximum (HTM) and the Medieval Climate Anomaly (MCA). Sedimentary phosphorus release has been implicated as a key driver of these events, but previous paleoenvironmental reconstructions have lacked the sampling resolution to investigate feedbacks in past iron-phosphorus cycling on short timescales. Here we employ Laser Ablation (LA)-ICP-MS scanning of sediment cores to generate ultra-high resolution geochemical records of past hypoxic events. We show that in-phase multidecadal oscillations in hypoxia intensity and iron-phosphorus cycling occurred throughout these events. Using a box model, we demonstrate that such oscillations were likely driven by instabilities in the dynamics of iron-phosphorus cycling under preindustrial phosphorus loads, and modulated by external climate forcing. Oscillatory behavior could complicate the recovery from hypoxia during future trajectories of external loading reductions.Peer reviewe

Sedimentary molybdenum and uranium : Improving proxies for deoxygenation in coastal depositional environments

Sedimentary molybdenum (Mo) and uranium (U) enrichments are widely used to reconstruct changes in bottom water oxygen conditions in aquatic environments. Until now, most studies using Mo and U have focused on restricted suboxic-euxinic basins and continental margin oxygen minimum zones (OMZs), leaving mildly reducing and oxic (but eutrophic) coastal depositional environments vastly understudied. Currently, it is un-known: (1) to what extent Mo and U enrichment factors (Mo-and U-EFs) can accurately reconstruct oxygen conditions in coastal sites experiencing mild deoxygenation, and (2) to what degree secondary (depositional environmental) factors impact Mo-and U-EFs. Here we investigate 18 coastal sites with varying bottom water redox conditions, which we define by means of five "redox bins", ranging from persistently oxic to persistently euxinic, from a variety of depositional environments. Our results demonstrate that Mo-and U-EF-based redox proxies and sedimentary Mo and U contents can be used to differentiate bottom water oxygen concentration among a range of modern coastal depositional environments. This is underpinned by the contrasting EFs of Mo and U along the redox gradient, which shows a substantial difference of Mo-EFs between redox bins 3-5 (ir/ regularly suboxic - ir/regularly dysoxic - persistently oxic) and of U-EFs between redox bins 1-2 (persistently euxinic - ir/regularly euxinic). Surprisingly, we observe comparatively low redox proxy potential for U in en-vironments of mild deoxygenation (redox bins 3-5). Further, we found that secondary factors can bias Mo-and U-EFs to such an extent that EFs do not reliably reflect bottom water redox conditions. We investigate the impact of limited Mo sedimentary sequestration in sulfidic depositional environments (i.e., the "basin reservoir effect", equilibrium with FeMoS4), Fe/Mn-(oxy)(hydr)oxide "shuttling", oxidative dissolution, the sulfate methane transition zone in the sediment, sedimentation rate, and the local Al background on Mo-and U-EFs.Peer reviewe