Polonium-210 and Lead-210 activities measured on 9 water bottle profiles during POLARSTERN cruise ANT-XXIV/3

As part of the GEOTRACES Polarstern expedition ANT XXIV/3 (ZERO and DRAKE), Polonium-210 and Lead-210 have been measured in the water column and on suspended particulate matter in February to April 2008. Our goal was to resolve the affinities of 210Po and 210Pb to transparent exopolymer particles (TEP) and particulate organic carbon (POC). Polonium-210 and Lead-210 in the ocean can be used to identify the sources and sinks of suspended matter. In seawater, Polonium-210 (210Po) and Lead-210 (210Pb) are produced by stepwise radioactive decay of Uranium-238. 210Po (138 days half life) and 210Pb (22.3 years half life) have high affinities for suspended particles. Those radionuclides are present in dissolved form and adsorbed onto particles. Following adsorption onto particle surfaces, 210Po especially is transported into the interior of cells where it bonds to proteins. In this way, 210Po also accumulates in the food chain. 210Po is therefore considered to be a good tracer for POC, and traces particle export over a timescale of months. 210Pb (22.3 years half life) adsorbs preferably onto structural components of cells, biogenic silica and lithogenic particles, and is therefore a better tracer more rapidly sinking matter. Water samples were taken with Niskin bottles. Dissolved Polonium-210 and Lead-210 activities refer to the fraction < 1µm. Particulate Polonium-210 and Lead-210 refer to the activity on particles >1µm retained on nucleopore filters. Zooplankton retained on the filters was systematically removed as this study focused on phytoplankton and exudates. The data have been submitted to Pangaea following a Polonium-Lead intercalibration exercise organized by GEOTRACES, where the AWI lab results range within the data standard deviation from 10 participating labs.

Polonium-210 and Lead-210 activities measured on 17 water bottle profiles and 50 surface water samples during POLARSTERN cruise ARK-XXII/2

Polonium-210 and Lead-210 have been measured in the water column and on suspended particulate matter during the POLARSTERN cruise ARK-XXII/2. The data have been submitted to Pangaea following a Polonium-Lead intercalibration exercise organized by GEOTRACES, where the AWI lab results range within the data standard deviation from 10 participating labs. Polonium-210 and Lead-210 in the ocean can be used to identify the sources and sinks of suspended matter. In seawater, Polonium-210 (210Po) and Lead-210 (210Pb) are produced by stepwise radioactive decay of Uranium-238. 210Po (138 days half life) and 210Pb (22.3 years half life) have high affinities for suspended particles. Those radionuclides are present in dissolved form and adsorbed onto particles. Following adsorption onto particle surfaces, 210Po especially is transported into the interior of cells where it bonds to proteins. In this way, 210Po also accumulates in the food chain. 210Po is therefore considered to be a good tracer for POC, and traces particle export over a timescale of month. 210Pb (22.3 years half life) adsorbs preferably onto structural components of cells, biogenic silica and lithogenic particles, and is therefore a better tracer more rapidly sinking matter. Our goal during ARK XXII/2 was to trace pathways of particulate and dissolved matter leaving the Siberian Shelf. The pathways of particulate and dissolved matter will be followed by the combined use of 210Po and 234Th as a tracer pair (and perhaps 210Pb) for particle flux (Cai, P.; Rutgers van der Loeff, MM (2008) doi:10.1594/PANGAEA.708354). This information gathered from the water column will be complemented with the results of the 210Po-210Pb study in sea ice (Camara-Mor, P, Instituto de Ciencias del Mar-SCIC, Barcelona, Spain) to provide a more thorough picture of particle transport from the shelf to the open sea and from surface to depth.

Structural features in ODP Holes 128-794D and 128-799B

Numerous structural features occur in the Leg 128 cores from the Japan Sea. They include (1) gravity-induced structures such as slump folds, (2) dewatering structures comprising several sets of veins, and (3) larger faults and veins developed in the volcanic basement of the Yamato Basin as well as in the sedimentary rocks of the Oki Ridge and Kita-Yamato Trough. Gravity-induced structures, mainly slumps and associated faults, suggest the existence of paleoslopes and the dominance of gravitational tectonics during the early and middle Miocene, at the Pliocene/Pleistocene boundary, and during the Quaternary. Several types of mud-filled veins having various shapes were observed. These are especially abundant in the middle Miocene siliceous claystones and porcellanites from the Kita-Yamato Trough. They have been interpreted as dewatering conduits that formed preferentially in highly porous, water-saturated diatomaceous muds on a slope, because of episodic loss of sediment strength, collapse of the sediment framework, and consequent fluid migration. The central part of the vein serves once as a fluid conduit, whereas the transition between conduit-controlled and intergranular flow occurs at the branching extremities, with concentration of fines. The likely trigger responsible for the strength loss is seismic activity. Development of these veins, spatially and chronologically linked to small normal microfaults, implies an extensional regime having layer-parallel extension and a local bedding-parallel shear couple, probably the result of gravitational gliding. The brittle fractures found in Yamato Basin basement Hole 794D cores comprise joints, faults, and veins filled with chlorite-saponite, saponite, and calcite. They suggest a likely transpressive to transtensional regime around the early Miocene/ middle Miocene boundary, with a north-northeast-south-southwest compression alternating with a west-northwest-eastsoutheast extension. The faults from Site 799 cores on the Yamato Rise exhibit a prominent early Miocene-middle Miocene extensional environment, a late Miocene-early Pliocene phase of normal and strike-slip faulting, and a final phase that began during the latest Pliocene. Site 798, on the Oki Ridge, reveals faults that recorded a consistent extensional tectonic regime from Pliocene to the Holocene. These data support the pull-apart kinematic model for early Miocene-middle Miocene time, as regarding the stress regime deduced from the Yamato Basin basement fractures. The recent compression known in the eastern margin of the Japan Sea was not documented by compressive structures at any site. The late Miocene-early Pliocene faulting phase corresponds to a major and general reorganization of the stress distribution in the arc area. Evidence for rapid and main subsidence and synsedimentary extension of the Yamato Basin and Yamato Rise areas between 20 and 15 Ma, and the concomitant rotation of southwest Japan, raise the question of links between this opening and the Shimanto Belt collision in southwest Japan, between the arc and the Philippine Sea Plate.