Landfast sea-ice and platelet-layer thickness and conductivity of Atka Bay, Antarctica, December 2012

Ice shelves strongly impact coastal Antarctic sea-ice and the associated ecosystem through the formation of a sub-sea-ice platelet layer. Although progress has been made in determining and understanding its spatio-temporal variability based on point measurements, an investigation of this phenomenon on a larger scale remains a challenge due to logistical constraints and a lack of suitable methodology. In this study, we applied a laterally-constrained Marquardt-Levenberg inversion to a unique multi-frequency electromagnetic (EM) induction sounding dataset obtained on the landfast sea ice of Atka Bay, eastern Weddell Sea, in 2012. In addition to consistent fast-ice thickness and -conductivities along > 100 km transects; we present the first comprehensive, high resolution platelet-layer thickness and -conductivity dataset recorded on Antarctic sea ice. The reliability of the algorithm was confirmed by using synthetic data, and the inverted platelet-layer thicknesses agreed within the data uncertainty to drill-hole measurements. Ice-volume fractions were calculated from platelet-layer conductivities, revealing that an older and thicker platelet layer is denser and more compacted than a loosely attached, young platelet layer. The overall platelet-layer volume below Atka Bay fast ice suggests that the contribution of ocean/ice-shelf interaction to sea-ice volume in this region is even higher than previously thought. This study also implies that multi-frequency EM induction sounding is an effective approach in determining platelet layer volume on a larger scale than previously feasible. When applied to airborne multi-frequency EM, this method could provide a step towards an Antarctic-wide quantification of ocean/ice-shelf interaction.

Geochemistry on ferromanganese crusts and nodules from Green Bay, Lake Michigan

The differential solubility of ferromanganese oxides can lead to stratigraphic separation of iron and manganese. Results of chemical analysis of a sequence of ferromanganese nodules overlying iron-rich crusts in northern Green Bay show that selec¬tive ion transport is important in concentrating manganese and associated trace elements near the oxygenated water-sediment interface. Manganese carbonate, which cements ferromanganese nodules, occurs in dark-gray silty sands that are located adjacent to the organic-rich muds of southern Green Bay. These muds contain an average of approximately 3.5 ppm (6x10-5M) interstitial Mn with 2.8 meq/l carbonate alkalinity. Thermodynamic calculation shows that interstitial water approaches equilibrium with MnCO3 in the upper 10 cm of sediment. This carbonate has a composition (Mn73Ca22Fe5)CO3 and has been identified as rhodochrosite.

Plankton biomass, POC and PON concentrations, and sinking velocities during the 2008 spring diatom bloom in Disko Bay

Phytoplankton and copepod succession was investigated in Disko Bay, western Greenland from February to July 2008. The spring phytoplankton bloom developed immediately after the breakup of sea ice and reached a peak concentration of 24 mg chl a/m**3 2 wk later. The bloom was analyzed during 3 phases: the developing, the decaying, and the post-bloom phases. Grazing impact by the copepod community was assessed by 4 methods; gut fluorescence, in situ faecal pellet production, and egg and faecal pellet production from bottle incubations. Calanus spp. dominated the mesozooplankton community. They were present from the initiation of the bloom but only had a small grazing impact on the phytoplankton. Consequently, there was a close coupling between the spring phytoplankton bloom and sedimentation of particulate organic carbon (POC). Out of 1836 ±180 mg C/m**2/d leaving the upper 50 m, 60 % was phytoplankton based carbon (PPC). The composition and quality of the sedimenting material changed throughout the bloom succession from PPC dominance in the initial phase with a POC/PON ratio close to 6.6 to a dominance of amorphous detritus with a higher POC/PON ratio (>10) in the post-bloom phase. The succession and fate of the phytoplankton spring bloom was controlled by nitrogen limitation and subsequent sedimentation, while grazing-mediated flux by the Calanus-dominated copepod community played a minor role in the termination of the spring bloom of Disko Bay.

Biogeochemistry measurements in a mesocosm experiment in the Bay of Hopavagen, Norway, in August 2012

The goal of this work has been to examine the influence of upper ocean food web structure and functioning on both the natural and artificially enhanced sequestration of carbon within the ocean. Data obtained in the mesocosm experiment run in the Bay of Hopavågen in August 2012 are used to assess the extent to which organic matter produced within four different food webs is retained in the upper ocean food web versus remineralized back to carbon dioxide and inorganic nutrients (ammonium, dissolved silicon, phosphate) versus exported from the system in the form of rapidly sinking particles. The experiment was carried out in a set of 12 mesocosms covering, in triplicate, 2 different phytoplankton communities (diatom versus non-diatom) exposed to 2 different zooplankton communities (-copepod and +copepod). These starting conditions were established by first filling the bags, roughly simultaneously, with seawater from the Bay of Hopavågen. Mesozooplankton were then removed to the most complete extent possible immediately removed from half of the mesocosms through repeated vertical hauls of a plankton net (200 µm mesh). Nitrate and phosphate was added to half mesocosms daily to promote the growth of non-siliceous phytoplankton (e.g. dinoflagellates or coccolithophores). To the other half of the mesocosms, nitrate, phosphate, and silicate were added to promote the growth of diatoms. Material was allowed to settle and the two distinct phytoplankton populations were allowed to develop for 4 days, after which copepods collected from the Bay of Hopavågen were added back to the half of the N+P mesocosms and to the half of the N+P+Si mesocosms from which mesozooplankton had not been removed at the beginning. This yielded a set of four initial starting conditions (N+P-copepods, N+P+copepods, N+P+Si-copepods, and N+P+Si+copepods). In the primary mesocosms, samples for a set of core parameters were taken every time the mesocosms were sampled. Samples for particulates (PIC, BSi, POC, PON) were collected on GF/F or 0.4 µm polycarbonate.

Lignin and chemical elements in the surface layer of bottom sediments from the Kandalaksha Bay of the White Sea

Chemical composition of the upper layer of sediments (0-1 cm) in the Kolvits and Knazhaya inlets, and also in the deep-water part of the Kandalaksha Bay is considered. It is shown that silts are richer in Fe, TOC, and heavy metals, than sands. The highest concentration of these elements is found in sediments under mixing zones of riverine and sea waters. Correlations of P, Zn, Cd, and Cu with iron are high, and correlations of Pb and Cu with organic carbon are also high. Very high concentration of Pb in the Kandalaksha Bay indicate technogenic pollution of sediments. Lignin makes significant contribution to formation of organic matter in the sediments. Composition of lignin in bottom sediments of the Kandalaksha Bay is defined by composition of lignin in soils and aerosols. Vanillin and syringyl structures prevail in molecular composition of lignin in bottom sediments. Their sources are coniferous vegetations, soils, and mosses. Ratios of certain types of phenol compounds indicate pollution of the upper layer of sediments by technogenic lignin. Lead and copper correlate well with this technogenic lignin.

Phytoplankton composition and biomass and its fluorescence parameters in waters of the Nha Trang Bay, South China Sea

Species composition and abundance of phytoplankton and chlorophyll concentration were measured at three horizons of 9 stations in the Nha Trang Bay of the South China Sea in March 1998. Vertical distribution of fluorescence parameters, temperature and irradiance were measured in the 0-18 m layer of the water column at 21 stations. It was shown that according to biomass (B) and chlorophyll concentration (Chl) the Bay is mezotrophic. B and Chl in the water column increased seaward. Mean values of Chl in the southern part of the Bay exceeded those in northern part. Mean values of B were similar. B and Chl in the bottom layer exceeded ones in the upper layer. Diatoms dominated in species diversity and abundance. Diatom Guinardia striata made the main contribution to phytoplankton biomass. Similarity of phytoplankton was high. In the upper layer phytoplankton was photoinhibited during the most part of the light period, but at the bottom photosynthetic activity was high. Water column B varied in an order of magnitude during the daily cycle mainly because of B variations in the bottom layer due to tide flow.

(Table 1) Composition of manganese-iron accumulates in the Kiel Bay, western Baltic Sea

Manganese-iron accumulates in the Kiel Bay were investigated with regard to their occurence, chemical composition and formation. Three morphologically different types were identified: a) growth on mussels, b) spherical nodules (ca. 1-3 cm) and c) disshaped symetrical and asymetrical nodules (up to 10 cm). Average values from 110 accumulates representing the three types were: Mn 29.3%, Fe 10.0%, Co 77 ppm, Ni 97 ppm, Cu 21 ppm and Zn 340 ppm. Accumulates on mussels showed the highest trace metal concentrations. A growth rate of ca. 0.6 mm/yr for type (a) was estimated. Heavy metal concentrations were determined in ca. 60 sediment and 30 pore water samples, and in 110 Baltic sea water samples. During certain periods, large increases in Mn values (up to 400 (µg/l) were found in the deeper waters. These concentrations develop during periods of strong stagnant conditions in the sediments where dissolution of Mn oxides, and diffusion mobilizes the Mn into the overlying waters. The manganese is then reprecipitated close to the boundary of the O2-enriched surface waters. This critical O2-concentration was found to be 40% saturation. In the Kiel Bay, Mn-Fe-accumulates are found in a zone which marks the upper limit sometimes reached by the deep waters of lower O2-concentration. Additionally, the availability of larger particles (especially stones or mussels) on the sediment surface is necessary. These conditions are met in the Kiel Bay in a water depth of 20-28 m at several places.

Diatom biostratigraphy of the Kerguelen Plateau and Prydz Bay, Southern Ocean

Samples were examined for diatoms from 22 holes at 11 sites cored by ODP Leg 119 on the Kerguelen Plateau and in Prydz Bay, East Antarctica. Diatoms were observed in Oligocene through Holocene sediments recovered from the Kerguelen Plateau. The diatom flora from the Kerguelen Plateau is characterized by species such as Azpeitia oligocenica, Rocella gelida, Rocella vigilans, and Synedra jouseana in the Oligocene and Crucidenticula nicobarica, Denticulopsis hustedtii, Nitzschia miocenica, and Thalassiosira miocenica in the Miocene. This somewhat cosmopolitan assemblage gives way to a Pliocene and Holocene assemblage characterized by species such as Nitzschia kerguelensis, Thalassiosira inura, and Thalassiosira torokina, which are endemic to the Southern Ocean region. Samples examined from Prydz Bay are generally devoid of diatoms. The exception is Site 739, where diatoms occur sporadically in lower Oligocene and upper Miocene through Quaternary sediments. The Leg 119 diatom biostratigraphic results allow the development of a stratigraphic framework for the Indian sector of the Southern Ocean. This diatom zonation integrates diatom zonations developed previously for other sectors of the Southern Ocean. The zonation proposed here is based on biostratigraphic events of both geographically widespread and endemic species calibrated to the paleomagnetic stratigraphy. As such, this zonation has application throughout the Southern Ocean and allows correlation from the southern high latitudes to the low latitudes.