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source:https://aip.scitation.org/doi/10.1063/1.5035118

The Mn / Ca of calcium carbonate tests of living (rose-Bengal-stained) benthic foraminifera (Elphidium batialis, Uvigerina spp., Bolivina spissa, Nonionellina labradorica and Chilostomellina fimbriata) were determined in relation to pore water manganese (Mn) concentrations for the first time along a bottom water oxygen gradient across the continental slope along the NE Japan margin (western Pacific). The local bottom water oxygen (BWO) gradient differs from previous field study sites focusing on foraminiferal Mn / Ca and redox chemistry, therefore allowing further resolution of previously observed trends. The Mn / Ca ratios were analysed using laser ablation inductively coupled plasma-mass spectrometer (ICP-MS), allowing single-chamber determination of Mn / Ca. The incorporation of Mn into the carbonate tests reflects environmental conditions and is not influenced by ontogeny. The inter-species variability in Mn / Ca reflected foraminiferal in-sediment habitat preferences and associated pore water chemistry but also showed large interspecific differences in Mn partitioning. At each station, Mn / Ca ratios were always lower in the shallow infaunal E. batialis, occupying relatively oxygenated sediments, compared to intermediate infaunal species, Uvigerina spp. and B. spissa, which were typically found at greater depth, under more reducing conditions. The highest Mn / Ca was always recorded by the deep infaunal species N. labradorica and C. fimbriata. Our results suggest that although partitioning differs, Mn / Ca ratios in the intermediate infaunal taxa are promising tools for palaeoceanographic reconstructions as their microhabitat exposes them to higher variability in pore water Mn, thereby making them relatively sensitive recorders of redox conditions and/or bottom water oxygenation.

Hadal trenches are considered to act as depo-centers for organic material at the trench axis and host unique and elevated biomasses of living organisms as compared to adjacent abyssal plains. To explore the diagenetic activity in hadal trench environments we quantified in situ benthic O2 consumption rates and sediment characteristics from the trench axis of two contrasting trench systems in the Pacific Ocean; the Izu-Bonin Trench underlying mesotrophic waters and the Tonga Trench underlying oligotrophic waters. In situ oxygen consumption at the Izu-Bonin Trench axis site (9200 m; 746±103 µmol m−2 d−1; n=27) was 3-times higher than at the Tonga Trench axis site (10800 m; 225±50 µmol m−2 d−1; n=7) presumably reflecting the higher surface water productivity in the Northern Pacific. Comparing benthic O2 consumption rates measured in the central hadal Tonga Trench to that of nearby (60 km distance) abyssal settings (6250 m; 92±44 µmol m−2 d−1; n=16) revealed a 2.5 higher activity at the trench bottom. Onboard investigations on recovered sediment furthermore revealed that the prokaryotic abundance and concentrations of phytopigments followed this overall trend (i.e minimum values at the abyssal site followed by higher values from the Tonga and Izu-Bonin Trenches axis, respectively). Excess 210Pb profiles suggested that mass-wasting events contributed to the deposition of material enhancing the concentration of organic matter in the central trench as compared to the abyssal settings. Our results complement recent findings from the Challenger deep in the Mariana Trench area, which also revealed elevated diagenetic activity in the central trench underpinning the importance of hadal ecosystems for the deep sea carbon cycling.

Live (Rose-Bengal stained) deep-sea foraminiferal faunashave been studied at five stations between 500–2000-m depthalong the NE Japanese margin (western Pacific) tounderstand how complex environmental conditions (e.g.,oxygen depletion, organic matter) control their structure(i.e., diversity, standing stocks, and microhabitats). Allstations are characterized by silty sediments with no evidenceof recent physical disturbances. The three stations locatedbetween 760–1250 m are bathed by dysoxic bottom waters(,45 mmol/L). Although high organic-carbon contents arerecorded at all stations (.2.2% DW), only the oxygendepletedsites are characterized by higher concentrations ofsugars, lipids, and enzymatically hydrolysable amino acids(EHAA). Sedimentary contents in chlorophyllic pigmentsdecrease with water depth without any major change in theirfreshness (i.e., [Chl a/(Chl a + Pheo a)] ratios) . BothUvigerina akitaensis and Bolivina spissa are restricted to thestations bathed by dysoxic waters, proving their oxygendepletiontolerance. In such conditions, both phytophagoustaxa are obviously able to take advantage of labile organiccompounds (e.g., lipids and EHAA) contained in phytodetritus.Nonionella stella and Rutherfordoides cornuta survivein oxygen-depleted environments probably via alternativemetabolic pathways (e.g., denitrification ability) and a largeflexibility in trophic requirements. At stations where oxygenavailability is higher (i.e., .70 mmol/L in bottom water) andwhere bioavailable organic compounds are slightly lessabundant, diversity indices remain low, and more competitivespecies (e.g., Uvigerina curticosta, U. cf. U. graciliformis,Nonionella globosa, Nonionellina labradorica, and Elphidiumbatialis) are dominant.

On March 11th, 2011 the Mw 9.0 2011 Tohoku-Oki earthquake resulted in a tsunami which caused major devastation in coastal areas. Along the Japanese NE coast, tsunami waves reached maximum run-ups of 40 m, and travelled kilometers inland. Whereas devastation was clearly visible on land, underwater impact is much more difficult to assess. Here, we report unexpected results obtained during a research cruise targeting the seafloor off Shimokita (NE Japan), shortly (five months) after the disaster. The geography of the studied area is characterized by smooth coastline and a gradually descending shelf slope. Although high-energy tsunami waves caused major sediment reworking in shallow-water environments, investigated shelf ecosystems were characterized by surprisingly high benthic diversity and showed no evidence of mass mortality. Conversely, just beyond the shelf break, the benthic ecosystem was dominated by a low-diversity, opportunistic fauna indicating ongoing colonization of massive sand-bed deposits.

Foraminifers form an important link between bacteria and macrobenthos in natural food webs and thereby play a major role in biogeochemical cycling. There have been few studies conducted to clarify these relationships, although the biomass of foraminifera, particularly the soft-shelled monothalamous taxa, is high in the deep seas. Molecular tools are now being used to study evolution and genetic diversity in widely separated oceanic environments. However, the relationship between genetic diversity and the ambient environment is not well understood. To test the idea that environmental conditions can affect genetic diversity, we conducted molecular phylogenetic analyses based on clone analysis of environmental DNA for benthic foraminifers and environmental measurements in sediments from various oceanic environments. Monothalamous foraminifers were found in dysoxic (<45 μM), low-oxygen (<120 μM), and well-oxygenated (>120 μM) environments. The number of phylotypes was higher in the oxic environments of central Sagami Bay, Japan, and the east equatorial Pacific Ocean, than in the lower-oxygen areas of Sagami Bay. Phylotypes closely related to the genus Ovammina and some other saccamminids, as well as the calcareous genus Stainforthia, were preferentially found in lower dissolved-oxygen (DO) environments, while phylotypes of other saccamminids, Hippocrepinella, and an unidentified foraminiferal species, occurred at higher DO concentrations. Our analysis suggests that novel monothalamous phylotypes exist in habitats ranging from the sulfide-enriched environments of chemosynthetic ecosystems to those with high concentrations of DO as at the abyssal depths and in well-mixed bioturbated sediments.

Udgivelsesdato: Aug 2009, Abstract: We present and compare small sediment-water fluxes of O-2 determined with the eddy correlation technique, with in situ chambers, and from vertical sediment microprofiles at a 1450 m deep-ocean site in Sagami Bay, Japan. The average O-2 uptake for the three approaches, respectively, was 1.62 +/- 0.23 (SE, n = 7), 1.65 +/- 0.33 (n = 2), and 1.43 +/- 0.15 (n = 25) mmol m(-2) d(-1). The very good agreement between the eddy correlation flux and the chamber flux serves as a new, important validation of the eddy correlation technique. It demonstrates that the eddy correlation instrumentation available today is precise and can resolve accurately even very small benthic O-2 fluxes. The correlated fluctuations in vertical velocity and O-2 concentration that give the eddy flux had average values of 0.074 cm s(-1) and 0.049 mu M. The latter represents only 0.08% of the 59 mu M mean O-2 concentration of the bottom water. Note that these specific fluctuations are average values, and that even smaller variations were recorded and contributed to the eddy flux. Our findings demonstrate that the eddy correlation technique is a highly attractive alternative to traditional flux methods for measuring even very small benthic O-2 fluxes.

On the basis of in situ NO3- microprofiles and chamber incubations complemented by laboratory-based assessments of anammox and denitrification we evaluate the nitrogen turnover of an ocean margin sediment at 1450-m water depth. In situ NO3- profiles horizontally separated by 12 mm reflected highly variable NO3- penetration depths, NO3- consumption rates, and nitrification. On average the turnover time of the pore-water NO3- pool was similar to 0.2 d. Net release of NH4+ during mineralization (0.95 mmol m(-2) d(-1)) sustained a net efflux of ammonia (53%), nitrification (24%), and anammox activity (23%). The sediment had a relatively high in situ net influx of NO3- (1.44 mmol m(-2) d(-1)) that balanced the N-2 production as assessed by onboard tracer experiments. N2 production was attributed to prokaryotic denitrification (59%), anammox (37%), and foraminifera-based denitrification (4%). Anammox thereby represented an important nutrient sink, but the N2 production was dominated by denitrification. Despite the fact that NO3- stored inside foraminifera represented similar to 80% of the total benthic NO3- pool, the slow intracellular NO3- turnover that, on average, sustained foraminifera metabolism for 12-52 d, contributed only to a minor extent to the overall N-2 production. The microbial activity in the surface sediment is a net nutrient sink of similar to 1.1 mmol N m(-2) d(-1), which aligns with many studies performed in coastal and shelf environments. Continental margin areas can act as significant N sinks and play an important role in regional N budgets.