Shallow water masses and their connectivity along the southern Australian continental margin

Four water masses are identified and described using hydrographic, nutrient and stable isotope data for the top 1000 m water depth of the southern Australian continental margin, from Cape Leeuwin to Tasmania. Three are identified from previous literature on the southeast Indian Ocean: Subtropical Surface Water (STSW), Tasmanian Subantarctic Mode Water (TSAMW) and Tasmanian Intermediate Water (TIW), and one is newly identified and named: South Australian Basin Central Water (SABCW). STSW (0–250 m) is transported east by the Leeuwin Current System and is modified by heating and evaporation along the subtropical continental shelf. SABCW (250–400 m) and TSAMW (400–650 m) form southwest of Tasmania from deep winter mixing in the region: SABCW at the Subtropical Front and TSAMW north of the Subantarctic Front. TIW (>650 m) forms southwest of Tasmania from mixing of warm, saline Antarctic Intermediate Water from the Tasman Sea and cool, fresh Antarctic Intermediate Water from the Antarctic Circumpolar Current. SABCW, TSAMW and TIW are transported west along the slope by the Flinders Current System, here defined as the western slope-trapped Flinders Current, Tasman Outflow and equatorward Sverdrup transport. Water mass distributions on the slope identify the interface between subantarctic water from the Southern Ocean and subtropical water transported by the Leeuwin Current System. This interface is ~300 m during winter and ~250 m during summer, but can be 150 m during summer in upwelling regions and off western Tasmania. Furthermore, stable isotope data of the water masses south and west of Australia show connectivity between the Subantarctic Zone, the southern Australian margin and the western Australian margin

Modern estuarine siliceous spiculites, Tasmania, Australia : a non-polar link to phanerozoic spiculitic cherts

Biosiliceous sedimentary rocks are well known from the geologic record and many are correctly interpreted to have formed in deepwater or cold-water environments. Shallow non-polar spiculites are also known from the rock record, yet no modern analog has been documented for such environments. Bathurst Harbour, an estuarine system in southwest Tasmania, provides this much-needed modern analog. In this system a sharp halocline separates tannin-rich low-salinity surface waters from clear marine bottom waters. Tannins supply few nutrients and substantially reduce light penetration to bottom environments, resulting in a thinned photic zone and the mixing of deeper-water subphotic biotas of soft corals, bryozoans, and sponges with other organisms more typical of this temperate shallow-water environment. The well-defi ned halocline allows a typically marine biota, including echinoderms, to live in bottom waters of this estuarine setting. The bio clastic factory, producing both carbonate and siliceous particles, exists in marine subphotic bottom waters of incised channel and shallow rocky environments along the shoreline. Extensive organic-rich soft sediments in protected embayments generate few bioclasts, but contain allochthonous sponge spicules transported from the adjacent bioclastic factory. Trapping of organic material within the estuarine system lowers sediment pH and promotes dissolution of carbonate biofragments, resulting in preferential preservation of siliceous sponge spicules. This situation implies that many biosiliceous neritic deposits in the rock record may be the result of similar preferential preservation

Trace element profiles as unique identifiers of western sandpiper (Calidris mauri) populations

Understanding the ecology and evolution of migratory animals requires information on how populations are geographically linked between periods of the annual cycle. To examine whether trace elements could be used to track migratory birds, we analyzed concentrations of 42 trace elements in feathers of western sandpipers (Calidris mauri (Cabanis, 1857)) that were grown at five different wintering sites ranging from San Francisco Bay (USA) to the Bay of Panama. Linear discriminant analysis of 15 elements correctly classified all 26 individuals to their wintering sites, including two sites that were separated by less than 3 km. A randomization procedure confirmed the robustness of these findings. Our analysis suggests that trace elements can be used to assign individuals to specific sites of origin. Although we did not sample feathers from all wintering areas, the regions our sites represented comprised a significant percentage of the global population. However, since trace element profiles appear to be highly specific to geographic sites, we suggest that this technique is best suited for cases where samples can be obtained from the majority of populations throughout a species range. Thus, under certain circumstances, trace element profiles may provide the potential to identify populations with a high degree of spatial accuracy

Modern estuarine siliceous spiculites, Tasmania, Australia : a non-polar link to phanerozoic spiculitic cherts

Biosiliceous sedimentary rocks are well known from the geologic record and many are correctly interpreted to have formed in deepwater or cold-water environments. Shallow non-polar spiculites are also known from the rock record, yet no modern analog has been documented for such environments. Bathurst Harbour, an estuarine system in southwest Tasmania, provides this much-needed modern analog. In this system a sharp halocline separates tannin-rich low-salinity surface waters from clear marine bottom waters. Tannins supply few nutrients and substantially reduce light penetration to bottom environments, resulting in a thinned photic zone and the mixing of deeper-water subphotic biotas of soft corals, bryozoans, and sponges with other organisms more typical of this temperate shallow-water environment. The well-defi ned halocline allows a typically marine biota, including echinoderms, to live in bottom waters of this estuarine setting. The bio clastic factory, producing both carbonate and siliceous particles, exists in marine subphotic bottom waters of incised channel and shallow rocky environments along the shoreline. Extensive organic-rich soft sediments in protected embayments generate few bioclasts, but contain allochthonous sponge spicules transported from the adjacent bioclastic factory. Trapping of organic material within the estuarine system lowers sediment pH and promotes dissolution of carbonate biofragments, resulting in preferential preservation of siliceous sponge spicules. This situation implies that many biosiliceous neritic deposits in the rock record may be the result of similar preferential preservation

Stable isotopes of carbon reveal flexible pairing strategies in a migratory Arctic bird

Many birds change their partners every year and pairing may occur before arrival on the breeding grounds. Early pairing strategies can benefit mates by strengthening pair-bonds and increasing the rate of pre-breeding resource acquisition, leading to increased reproductive output and success, especially for migratory species breeding in seasonally-constrained environments like the Arctic. Despite the theorized and documented advantages of early pairing, we know rather little about pairing phenology in many species. Here, we test the use of a stable isotope (carbon δ 13 C) method to assign geographic origin of paired birds to examine pairing phenology in Arctic-breeding Common Eiders (Somateria mollissima borealis). During two consecutive years, we captured paired individuals upon their arrival at breeding grounds approximately 2–3 weeks before laying. Pairs with similar δ 13 C in their claws indicates that they paired during winter, while similar blood values (with no similarity in claws) would reveal pairs formed much later, during the pre-breeding period near or on the breeding grounds. While a large proportion of pairs (43%) appeared to pair on wintering grounds, an almost equal number (52%) likely paired within 1 month prior to arrival on the breeding grounds. The remaining 5% did not have an obvious pairing time. Despite this variability in pairing phenology, we found no significant differences in body condition between females or males which paired in winter or spring. In the year characterized with more challenging winter conditions, pairs formed in spring tended to have a higher breeding propensity than those formed in winter, although there were no