Nighttime dissolution in a temperate coastal ocean ecosystem increases under acidification

Anthropogenic emissions of carbon dioxide (CO2) are causing ocean acidification, lowering seawater aragonite (CaCO3) saturation state (Omega arag), with potentially substantial impacts on marine ecosystems over the 21st Century. Calcifying organisms have exhibited reduced calcification under lower saturation state conditions in aquaria. However, the in situ sensitivity of calcifying ecosystems to future ocean acidification remains unknown. Here we assess the community level sensitivity of calcification to local CO2-induced acidification caused by natural respiration in an unperturbed, biodiverse, temperate intertidal ecosystem. We find that on hourly timescales nighttime community calcification is strongly influenced by Omega arag, with greater net calcium carbonate dissolution under more acidic conditions. Daytime calcification however, is not detectably affected by Omega arag. If the short-term sensitivity of community calcification to Omega arag is representative of the long-term sensitivity to ocean acidification, nighttime dissolution in these intertidal ecosystems could more than double by 2050, with significant ecological and economic consequences.

TOC, TN, and sedimentary d15N and d13C ratios of sediment core SO201-2-85

We present high-resolution records of sedimentary nitrogen (d15Nbulk) and carbon isotope ratios (d13Cbulk) from piston core SO201-2-85KL located in the western Bering Sea. The records reflect changes in surface nitrate utilization and terrestrial organic matter contribution in submillennial resolution that span the last 180 kyr. The d15Nbulk record is characterized by a minimum during the penultimate interglacial indicating low nitrate utilization (~62-80%) despite the relatively high export production inferred from opal concentrations along with a significant reduction in the terrestrial organic matter fraction (mterr). This suggests that the consumption of the nitrate pool at our site was incomplete and even more reduced than today (~84%). d15Nbulk increases from Marine Isotope Stage (MIS) 5.4 and culminates during the Last Glacial Maximum, which indicates that nitrate utilization in the Bering Sea was raised during cold intervals (MIS 5.4, 5.2, 4) and almost complete during MIS 3 and 2 (~93-100%). This is in agreement with previous hypotheses suggesting that stronger glacial stratification reduced the nutrient supply from the subeuphotic zone, thereby increasing the iron-to-nutrient ratio and therefore the nitrate utilization in the mixed surface layer. Large variations in d15Nbulk were also recorded from 180 to 130 ka BP (MIS 6), indicating a potential link to insolation and sea-level forcing and its related feedbacks. Millennial-scale oscillations were observed in d15Nbulk and d13Cbulk that might be related to Greenland interstadials.

Location and ages of terrestrial peatlands located on continental shelves and in coastal sediments

This synthesis dataset contains records of freshwater peat and lake sediments from continental shelves and coastal areas. Information included is site location (when available), thickness and description of terrestrial sediments as well as underlying and overlying sediments, dates (when available), and references.

Age determinations of bottom sediments from the Sea of Okhotsk by different methods

On the base of data on benthic foraminifera and sediment biogeochemistry (contents of total organic carbon, calcium carbonate and biogenic opal) in two cores (1265 and 1312 m water depth) from the southeastern Sakhalin slope and one core (839 m water depth) from the southwestern Kamchatka slope variations of the oxygen minimum zone during the last 50 ka in the Okhotsk Sea are reconstructed. The oxygen minimum zone was less pronounced during cooling in the MIS 2 that is suggested to be caused by maximal expansion of the sea ice cover, decrease of marine productivity and increase of production of oxygenated Okhotsk Sea Intermediate Water (OSIW). Two-step-like strengthening of oxygen minimum zone during warmings in the Terminations 1a and 1b was combined with (1) enhanced oxygen consumption due to decomposition of large amount of organic matter in the water column and bottom sediments due to increased marine productivity and supply of terrigenous material from submerged northern shelves; (2) sea ice cover retreat and reduction of OSIW production; (3) freely inflow of the oxygen-depleted intermediate water mass from the North Pacific.

Laminated sediment cores in the Bering Sea

During the last glacial termination, the upper North Pacific Ocean underwent dramatic and rapid changes in oxygenation that lead to the transient intensification of oxygen minimum zones (OMZs), recorded by the widespread occurrence of laminated sediments on circum-Pacific continental margins. We present a new laminated sediment record from the mid-depth (1100 m) northern Bering Sea margin that provides insight into these deglacial OMZ maxima with exceptional, decadal-scale detail. Combined ultrahigh-resolution micro-X-ray-fluorescence (micro-XRF) data and sediment facies analysis of laminae reveal an alternation between predominantly terrigenous and diatom-dominated opal sedimentation. The diatomaceous laminae are interpreted to represent spring/summer productivity events related to the retreating sea ice margin.We identified five laminated sections in the deglacial part of our site. Lamina counts were carried out on these sections and correlated with the Bølling-Allerød and Preboreal phases in the North Greenland Ice Core (NGRIP) oxygen isotope record, indicating an annual deposition of individual lamina couplets (varves). The observed rapid decadal intensifications of anoxia, in particular within the Bølling-Allerød, are tightly coupled to short-term warm events through increases in regional export production. This dependence of laminae formation on warmer temperatures is underlined by a correlation with published Bering Sea sea surface temperature records and d18O data of planktic foraminifera from the Gulf of Alaska. The rapidity of the observed changes strongly implies a close atmospheric teleconnection between North Pacific and North Atlantic regions.We suggest that concomitant increases in export production and subsequent remineralization of organic matter in the Bering Sea, in combination with oxygen-poor waters entering the Being Sea, drove down oxygen concentrations to values below 0.1ml/l and caused laminae preservation. Calculated benthic-planktic ventilation ages show no significant variations throughout the last deglaciation, indicating that changes in formation rates or differing sources of North Pacific mid-depth waters are not prime candidates for strengthening the OMZ at our site. The age models established by our correlation procedure allow for the determination of calendar age control points for the Bølling-Allerød and the Preboreal that are independent of the initial radiocarbon-based chronology. Resulting surface reservoir ages range within 730-990 yr during the Bølling-Allerød, 800-1100 yr in the Younger Dryas, and 765-775 yr for the Preboreal.

(Table 2) Age determination of brock-red sandy mud beds and detrital carbonate beds in the Scotian margin

Piston cores from the continental margin off Nova Scotia show up to four discrete intervals of "brick-red sandy mud", which are up to 20 cm thick. The ages of these intervals are bracketed by several radiocarbon dates, and three fall in the range 12.5-14.1 ka (radiocarbon years with -0.4 kyr reservoir correction). The youngest dates from ~10.4 ka, placing it within the Younger Dryas. The distribution of the beds and their petrographic character indicate a source in the Gulf of Saint Lawrence. The grain size of these beds suggests that they comprise a coarse component transported by ice rafting that diminishes distally and a fine component that represents suspension fallout from a surface plume and resulting nepheloid layers. Graded brick-red beds in some cores were probably redeposited from turbidity currents. The lowermost bed on the Laurentian Fan and East Scotian Rise is immediately overlain by a carbonate-rich interval that can be identified all around the margin of the Grand Banks. This interval is correlated with detrital carbonate bed DC-1 in the Labrador Sea and Heinrich event H1 in the North Atlantic. The sequential occurrence of the two beds suggests that they may be a response to the same trigger, probably sea level rise, but that the Gulf of Saint Lawrence source was more easily destabilized.