Iodine speciation at time series station DYFAMED

Iodine speciation analysis was carried out upon seawater samples collected in July 1993 at the DYFAMED station (43 °25?N, 7 °52?E) located in the northwestern Mediterranean Sea. Dissolved iodate and iodide were directly determined by differential pulse polarography and cathodic stripping square wave voltammetry, respectively, and organically bound iodine was estimated by wet-chemical oxidation with sodium hypochlorite. Iodate is the predominant species ranging from 416 nM in surface waters to 480 nM in bottom waters. Iodide is present in significant concentrations up to 60 nM in surface waters, undetectable between 500 and 1000 m depth and present in very low but measurable concentrations (about 6 nM) in deep waters. The vertical profile of total free iodine demonstrates observable removal from surface waters, slight enrichment at about 200 m depth and constant there below. Up to 40 nM of organically bound iodine has been estimated between 20 to 30 m. Factorial analysis of different iodine species with biologically relevant parameters provided strong evidence for iodine biophilic features.

Depth profiles of iodide and iodate during POLARSTERN cruise ANT-XXIV/3 to the Atlantic sector of the Southern Ocean

The biogeochemistry of iodine in the waters of the Atlantic sector of the Southern Ocean was investigated during the Polarstern cruise ANTXXIV-3 ZERO&DRAKE. The speciation and distribution of iodine (iodate and iodide) in seawater was examined across gradients of iron concentrations and phytoplankton abundance, ranging from an open ocean region along the Zero Meridian to the Weddell Sea and Drake Passage. Iodine cycling in high latitudes differs from that in low latitudes due to differences in the plankton community composition and the physicochemical characteristics. Iodate concentrations ranged between 400 and 450 nmol/L from the surface to the bottom. Surface concentrations of iodide (17 to over 60 nmol/L) were about an order of magnitude higher than below the pycnocline. The peak values of iodide lay nearly always within the euphotic zone and showed a weak, positive correlation with nitrite concentrations in the upper 200 m. In all vertical profiles a pronounced sub-surface maximum in iodide appears between 50 and 200 m depth indicating an iodide drawdown at the near surface. Iodide distribution in the Weddell Sea showed elevated levels in Weddell Sea Bottom Water (WSBW) indicating slow oxidation kinetics and the potential for iodide as a tracer of WSBW formation.

Sediment wave layer summary in ODP Site 172-1062

Abyssal mud waves (or fine-grained sediment waves) are often cited as evidence for deep current activity because subbottom profiles show that the wave form has migrated with time. The migration history of a fine-grained sediment wave on the Blake-Bahama Outer Ridge (ODP Site 1062) has been studied through the analysis of multiple ODP holes spaced across the wave. Additional information about wave migration patterns comes from 3.5-kHz records and watergun seismic profiles. These data suggest that wave migration has varied during the last not, vert, similar ~10 Myr, although the only sediments sampled are younger than 4.8 Ma. Seismic profiles suggest wave migration was initiated about 8-10 Ma, and wave migration was pronounced from about 5 Ma to about 1 Ma (with an episode of wave reorganization about 4.5 Ma). Analysis of ODP cores suggests that migration rates have been somewhat lower and more variable during the last 1 Myr. Intervals of no wave migration are observed for several time intervals and appear to characterize deglaciations, especially during the last 500 kyr. Comparisons between seismic profiles and the core record show that most of the seismic horizons correlate closely with time horizons, and thus that the seismic profiles give a reasonable representation of sediment wave migration. Models suggest that wave migration is more pronounced during periods of higher bottom current flow and less pronounced during periods of lower current flow. Thus the migration record is consistent with generally higher bottom flow speeds at this site prior to 1 Ma and lower bottom flow speeds after 1 Ma. The Mid-Pleistocene Transition from a dominant climatic periodicity of 40 kyr to a dominant climatic periodicity of 100 kyr starts at about this time, suggesting an overall reduction in bottom flow speed at this site coincident with changing climate patterns. These changes in flow speed could be related to changes in the depth of the Western Boundary Undercurrent as well as to changes in the speed of thermohaline circulation.

Wave-induced changes in seaweed toughness entail plastic modifications in snail traits maintaining consumption efficacy, link to supplementary material

1. Environmental stress can influence species traits and performance considerably. Using a seaweed-snail system from NW (Nova Scotia) and NE (Helgoland) Atlantic rocky shores, we examined how physical stress (wave exposure) modulates traits in the seaweed Fucus vesiculosus and indirectly in its main consumer, the periwinkle Littorina obtusata. 2. In both regions, algal tissue toughness increased with wave exposure. Reciprocal-transplant experiments showed that tissue toughness adjusts plastically to the prevailing level of wave exposure. 3. Choice experiments tested the feeding preference of snails from sheltered, exposed, and very exposed habitats for algae from such wave exposures. Snails from exposed and very exposed habitats consumed algal tissues at similar rates irrespective of the exposure of origin of the algae. However, snails from sheltered habitats consumed less algal tissues from very exposed habitats than tissues from sheltered and exposed habitats. Choice assays using reconstituted algal food (triturated during preparation) identified high thallus toughness as the explanation for the low preference of snails from sheltered habitats for algae from very exposed habitats. 4. Ultrastructural analyses of radulae indicated that rachidian teeth were longest and the number of cusps in lateral teeth (grazing-relevant traits) was highest in snails from very exposed habitats, suggesting that radulae are best suited to rupture tough algal tissues in such snails. 5. No-choice feeding experiments revealed that these radular traits are also phenotypically plastic, as they adjust to the toughness of the algal food. 6. Synthesis. This study indicates that the observed plasticity in the feeding ability of snails is mediated by wave exposure through phenotypic plasticity in the tissue toughness of algae. Thus, plasticity in consumers and their resource species may reduce the potential effects of physical stress on their interaction.