Otolith microstructure and trace elemental concentrations in juvenile Pacific bluefin tuna (Thunnus orientalis) caught off of Southern California in 2012

We combined longitudinal analyses of otolith microstructure and trace elemental composition in ~ age 1-2 Pacific bluefin tuna (PBT, n = 24) for inferring the arrival of individuals in the California Current Large Marine Ecosystem (CCLME). Element:Ca ratios in transverse otolith sections (9-12 rows, triplicate ablations from coreprimordium to edge, ø50 µm) were quantified for eight elements: Li, Mg, Mn, Co, Cu, Zn, Sr, and Ba, which was followed by microstructure analysis to provide age estimates corresponding to each ablation spot. Age estimates from otoliths ranged from 328 to 498 days post hatch. The combined elemental signatures of four elements (Ba, Mg, Co, Cu) showed a significant increase at the otolith edge in approximately half of the individuals (30-60 days prior to catch). Given the different oceanographic properties of oligotrophic open Pacific vs. high nutrient, upwelling CCLME waters, this signal is consistent with the entry of the fish into the CCLME, which was estimated to occur primarily in July after a transoceanic migration of ~1.5-2.0 months.

Geochemistry of the water column of southern lake Baikal during 1967-2005

At present, when the influence of human economic activity is progressively increasing, significant attention is devoted to the state of water ecosystems. All researchers engaged in these problems agree that the state of the water system (pollution and eutrophication) can only be estimated on the basis of long-term researches. Systemic monitoring (at least once per month) of ionic components (Ca2+, Mg2+, Na+, K+, bicarbonates, sulfates, and chlorides) in unfiltered water of Lake Baikal and its tributaries had been carried out under the supervision of Votintsev since 1947. Based on the analysis of systematic data on trophic components obtained during 1965-2005, we tried to estimate the present-day trophic status of the pelagic zone in the lake, define the trend of long-term changes of trophic components and understand the reasons of the distortion of cyclicity in the development of spring diatom algae, which create a favorable environment in any water basin. It should be noted that the station near Cape Polovinnyi is located 20 km away from the town of Baikal'sk. Wastewaters of the Baikal'sk pulp and paper mill is the main source of dioxins and furans in Baikal. Based on the significant difference between sulfate contents in wastewaters of the plant (>300 mg/l), tributaries of Baikal (7.5 mg/l), and waters in the southern part of the lake (3.9 mg/l), we defined the following periods: (i) period of natural seasonal patterns until 1967-1968 (prior to putting the Baikal'sk Mill into operation; (ii) period of weak anthropogenic pollution (1969-1985); and (iii) period of strong anthropogenic pollution since 1986.

Sea surface reconstruction for sediments of the California continental margin

Organic matter in sediment samples from three ODP sites (Ocean Drilling Program Leg 167) that form a south-north transect was investigated to reconstruct the paleoclimatic and oceanographic conditions on the California continental margin during the last 160 kyr. Alkenone-derived paleosea surface temperatures (SST) are 3 to 6°C colder in glacial stages and reveal a clear relationship with global climate changes; the differences are greater in the north. Latitudinal SST comparison exhibits water mixing of the colder California Current with warmer waters from the south, particularly in the southern central California borderland area. Organic matter accumulation on the California continental margin indicates an interplay between climatic and atmospheric glacial-interglacial variations and spatially and temporally changing nutrient availability along the California coastline. Climatic and atmospheric dependent circulations apparently caused variations in the intensity of coastal upwelling along the southern central California margin and this suggests, due to the close connection of the California Current to the local wind patterns, that the California Current was weaker during glacial and stronger during interglacial periods.

Planktic foraminiferal abundance and stable oxygen isotope ratios of sediment cores from the Southern California Borderlands

A variety of evidence suggests that average sea surface temperatures (SSTs) during the last glacial maximum in the California Borderlands region were significantly colder than during the Holocene. Planktonic foraminiferal delta18O evidence and average SST estimates derived by the modern analog technique indicate that temperatures were 6°-10°C cooler during the last glacial relative to the present. The glacial plankton assemblage is dominated by the planktonic foraminifer Neogloboquadrina pachyderma (sinistral coiling) and the coccolith Coccolithus pelagicus, both of which are currently restricted to subpolar regions of the North Pacific. The glacial-interglacial average SST change determined in this study is considerably larger than the 2°C change estimated by Climate: Long-Range Investigation, Mapping, and Prediction (CLIMAP) [1981]. We propose that a strengthened California Current flow was associated with the advance of subpolar surface waters into the Borderlands region during the last glacial.

(Table 2) Integrated concentration, production and dissolution of silica in the water column of the southern Pacific

An intense diatom bloom developed within a strong meridional silicic acid gradient across the Antarctic Polar Front at 61°S, 170°W following stratification of the water column in late October/early November 1997. The region of high diatom biomass and the silicic acid gradient propogated southward across the Seasonal Ice Zone through time, with the maximum diatom biomass tracking the center of the silicic acid gradient. High diatom biomass and high rates of silica production persisted within the silicic acid gradient until the end of January 1998 (ca. 70 d) driving the gradient over 500 km to the south of its original position at the Polar Front. The bloom consumed 30 to >40 µM Si(OH)4 in the euphotic zone between about 60 and 66°S leaving near surface concentrations <2.5 µM and occasionally <1.0 µM in its wake. Integrated biogenic silica concentrations within the bloom averaged 410 mmol Si/m**2 (range 162-793 mmol Si/m**2). Average integrated silica production on two consecutive cruises in December 1997 and January 1998 that sampled the bloom while it was well developed were 27.5±6.9 and 22.6±20 mmol Si/m**2/d, respectively. Those levels of siliceous biomass and silica production are similar in magnitude to those reported for ice-edge diatom blooms in the Ross Sea, Antarctica, which is considered to be among the most productive regions in the Southern Ocean. Net silica production (production minus dissolution) in surface waters during the bloom was 16-21 mmol Si/m**2/d, which is sufficient for diatom growth to be the cause of the southward displacement of the silicic acid gradient. A strong seasonal change in silica dissolution : silica production rate ratios was observed. Integrated silica dissolution rates in the upper 100-150 m during the low biomass period before stratification averaged 64% of integrated production. During the bloom integrated dissolution rates averaged only 23% of integrated silica production, making 77% of the opal produced available for export to depth. The bloom ended in late January apparently due to a mixing event. Dissolution : production rate ratios increased to an average of 0.67 during that period indicating a return to a predominantly regenerative system. Our observations indicate that high diatom biomass and high silica production rates previously observed in the marginal seas around Antarctica also occur in the deep ocean near the Polar Front. The bloom we observed propagated across the latitudinal band overlying the sedimentary opal belt which encircles most of Antarctica implying a role for such blooms in the formation of those sediments. Comparison of our surface silica production rates with new estimates of opal accumulation rates in the abyssal sediments of the Southern Ocean, which have been corrected for sediment focusing, indicate a burial efficiency of <=4.6% for biogenic silica. That efficiency is considerably lower than previous estimates for the Southern Ocean.

(Table T1) Pore water chemistry of ODP Site 195-1202 sediments, southern Okinawa Trough

Pore water was collected from sediment cores from Holes 1202A and 1202D in the southern Okinawa Trough during Ocean Drilling Program (ODP) Leg 195. Because drilling at this site was completed only a few hours out of port during the end of the leg, whole rounds of sediment core 5 or 10 cm long were sealed and stored at ~3°C until pore water could be extracted from them during Leg 196, using a titanium squeezer designed by Manheim and Sayles (1974) and standard handling techniques (Shipboard Scientific Party, 2002, doi:10.2973/odp.proc.ir.195.103.2002).

Geomicrobiology, bulk sediment characteristics and pore water chemistry of sediment cores from Laguna Potrok Aike, southern Patagonia

Authigenic minerals can form in the water column and sediments of lakes, either abiotically or mediated by biological activity. Such minerals have been used as paleosalinity and paleoproductivity indicators and reflect trophic state and early diagenetic conditions. They are also considered potential indicators of past and perhaps ongoing microbial activity within sediments. Authigenic concretions, including vivianite, were described in late glacial sediments of Laguna Potrok Aike, a maar lake in southernmost Argentina. Occurrence of iron phosphate implies specific phosphorus sorption behavior and a reducing environment, with methane present. Because organic matter content in these sediments was generally low during glacial times, there must have been alternative sources of phosphorus and biogenic methane. Identifying these sources can help define past trophic state of the lake and diagenetic processes in the sediments. We used scanning electron microscopy, phosphorus speciation in bulk sediment, pore water analyses, in situ ATP measurements, microbial cell counts, and measurements of methane content and its carbon isotope composition (d13C CH4) to identify components of and processes in the sediment. The multiple approaches indicated that volcanic materials in the catchment are important suppliers of iron, sulfur and phosphorus. These elements influence primary productivity and play a role in microbial metabolism during early diagenesis. Authigenic processes led to the formation of pyrite framboids and revealed sulfate reduction. Anaerobic oxidation of methane and shifts in pore water ion concentration indicated microbial influence with depth. This study documents the presence of active microbes within the sediments and their relationship to changing environmental conditions. It also illustrates the substantial role played by microbes in the formation of Laguna Potrok Aike concretions. Thus, authigenic minerals can be used as biosignatures in these late Pleistocene maar sediments.

Sediment and pore water geochemistry of sediment cores, Potter Cove, King George Island

Redox-sensitive trace metals (Mn, Fe, U, Mo, Re), nutrients and terminal metabolic products (NO3-, NH4+, PO43-, total alkalinity) were for the first time investigated in pore waters of Antarctic coastal sediments. The results of this study reveal a high spatial variability in redox conditions in surface sediments from Potter Cove, King George Island, western Antarctic Peninsula. Particularly in the shallower areas of the bay the significant correlation between sulphate depletion and total alkalinity, the inorganic product of terminal metabolism, indicates sulphate reduction to be the major pathway of organic matter mineralisation. In contrast, dissimilatory metal oxide reduction seems to be prevailing in the newly ice-free areas and the deeper troughs, where concentrations of dissolved iron of up to 700 µM were found. We suggest that the increased accumulation of fine-grained material with high amounts of reducible metal oxides in combination with the reduced availability of metabolisable organic matter and enhanced physical and biological disturbance by bottom water currents, ice scouring and burrowing organisms favours metal oxide reduction over sulphate reduction in these areas. Based on modelled iron fluxes we calculate the contribution of the Antarctic shelf to the pool of potentially bioavailable iron (Feb) to be 6.9x10**3 to 790x10**3 t/yr. Consequently, these shelf sediments would provide an Feb flux of 0.35-39.5/mg/m**2/yr (median: 3.8 mg/m**2/yr) to the Southern Ocean. This contribution is in the same order of magnitude as the flux provided by icebergs and significantly higher than the input by aeolian dust. For this reason suboxic shelf sediments form a key source of iron for the high nutrient-low chlorophyll (HNLC) areas of the Southern Ocean. This source may become even more important in the future due to rising temperatures at the WAP accompanied by enhanced glacier retreat and the accumulation of melt water derived iron-rich material on the shelf.

Interstitial-water geochemistry of Kerguelen Plateau sediments

This report synthesizes all of the interstitial-water chemistry studies associated with the Kerguelen Plateau phase of ODP Leg 119. Sediments were cored at six sites (49°24'S to 59°36'S) in water depths ranging from 564 to 4082 m. A total of 77 interstitial-water samples was recovered as part of the routine sampling protocol. In addition, a novel, highresolution pore-water sampling program was tested during Leg 119 that enabled us to pinpoint reaction zones and extend our data base to deeper, drier levels that were heretofore inaccessible. Data collected include interstitial-water sodium, potassium, calcium, magnesium, pH, alkalinity, sulfate, ammonia, phosphate, aqueous silica, salinity, chloride, oxidation-reduction potentials, and sediment chemistry. The northern sector (Sites 736 and 737) is characterized by the highest sedimentation rates (up to 140 m/m.y.) and thermal gradients (70°-98°C/km) encountered on the Kerguelen Plateau during Leg 119. Site 737 represents the most reactive sediment column cored on the Kerguelen Plateau. Major cation fluxes at Site 737 are the strongest measured during Leg 119. High dissolved calcium concentrations (141.5 mM) were encountered near the bottom of Hole 737B. Elevated temperatures promote silica diagenesis and the alteration of volcanic material below 300 mbsf, and a diagenetic front was discovered near 370 mbsf at Site 737. The southern portion of the Kerguelen Plateau (Sites 738 and 744) records the lowest sedimentation rates (less than 5 m/m.y.) and thermal gradients (43°C/km) of the three study areas. Major cation fluxes at the southern sites are the lowest that we measured on the Kerguelen Plateau. High-resolution sampling provided evidence for significant silica release to the pore waters during the weathering of basement basalt. The relatively low thermal gradient does not appear to be sufficient for the formation of the opal-CT and quartz chert beds and nodules that were encountered below 120 mbsf at Site 738. Sediment-accumulation rates on the Eastern Kerguelen Sediment Ridge (Sites 745 and 746) are intermediate to those of the northern and southern sites. Deposition below the regional CCD accounts for the nearly carbonate-free, siliceous sediments. Despite their low organic carbon contents (mean = 0.15%), sediments on the Eastern Kerguelen Sediment Ridge exhibit the highest pore-water alkalinity (6.77 mM), ammonium (0.50 mM), and phosphate (23 µM) concentrations measured on the Kerguelen Plateau. Major cation fluxes are intermediate to those calculated for the northern and southern sites. The Eastern Kerguelen Sediment Ridge interstitial waters are unusual, however, in that the downward flux of magnesium is greater than the upward flux of calcium.