Upwelling characteristics and nutrient enrichment of the Kangaroo Island upwelling region, South Australia

An analysis is presented of hydrographic and nutrient data collected over three years for the Kangaroo Island upwelling region, Lincoln Shelf, South Australia, to determine the signature of upwelled water, depth of upwelling and the source water mass being brought onto the shelf. Strong upwelling seasons were recorded during the 2007-2008 and 2009-2010 summers, while the summer of 2008-2009 had only one weak upwelling event. Strong upwelling events during February and March 2008 and February and March 2010 recorded temperatures and salinities as low as 10.44C and 34.85, and NOx and phosphate concentrations as high as 13.35 and 0.94 μmol/L, respectively, at 105 m on the shelf. Upwelled water properties matched slope water properties between 240 and 370 m, indicating water can be upwelled over depths of 200 m or more. Upwelling from these depths sources South Australian Basin Central Water of Southern Ocean origin, which is transported west along the slope by the Flinders Current System. New results for nutrients show average values of NOx and phosphate during months of strong upwelling to be 6.1 times and 4.6 times greater, respectively, than during winter months, and that upwelled water can have nutrient concentrations up to 90 times higher than those in summer surface waters. Strong relationships between temperature and nutrients on the slope can help estimate nutrient concentrations supplied to the shelf during upwelling events. Upwelled water was also low in silicate, a signature of Southern Ocean water masses, which has implications for phytoplankton community structure and diatom abundance on the shelf

Water masses and their seasonal variation on the Lincoln Shelf, South Australia

Five water masses are defined for the Lincoln Shelf, South Australia using hydrographic and stable isotope data. Three water masses are present on the shelf and slope year‐round. Slope Water with low temperature, salinity, and isotope values occurs perennially on the slope at depths greater than 180 m, and episodically upwells onto the shelf during summer. During strong upwelling events this water can be upwelled from 300 m to 100 m water depth on the shelf south of Kangaroo Island. This water then flows west toward Eyre Peninsula and into the mouth of Spencer Gulf. The most common shelf water is Subtropical Surface Water, a mixed water mass that is transported year‐round by the eastward flowing South Australian Current. This current is heavily influenced by waters from the Great Australian Bight and local modifications, with temperature and salinity of 16–17°C and 35.8, respectively. Local summer heating and evaporation of Subtropical Surface Water on the shelf and within Spencer Gulf forms Evaporated Water, a water mass with high temperature, salinity and isotope values. The use of stable isotopes in water mass analysis permits the identification of two new water masses that form on the shelf during summer. Mixed Slope Water forms when Slope Water mixes with Subtropical Surface Water during upwelling events, and Cooled Evaporated Water is generated when surface Evaporated Water mixes vertically with cool, fresh bottom waters. Such dynamics lead to mixing of nutrient‐rich mesotrophic upwelled waters with oligotrophic surface waters, which supports greater levels of primary productivity on the shelf.Financial support for the analyses was from grants from the Natural Sciences and Engineering Research Council Discovery program, the Canada Foundation for Innovation and the Ontario Innovation Trust (TKK, NPJ

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

Natal dispersal driven by environmental conditions interacting across the annual cycle of a migratory songbird

Natal dispersal, the process through which immature individuals permanently depart their natal area in search of new sites, is integral to the ecology and evolution of animals. Insights about the underlying causes of natal dispersal arise mainly from research on species whose short dispersal distances or restricted distributions make them relatively easy to track. However, for small migratory animals, the causes of natal dispersal remain poorly understood because individuals are nearly impossible to track by using conventional mark–recapture approaches. Using stable-hydrogen isotope ratios in feathers of American redstarts (Setophaga ruticilla) captured as immature birds and again as adults, we show that habitat use during the first tropical nonbreeding season appears to interact with latitudinal gradients in spring phenology on the temperate breeding grounds to influence the distance traveled on the initial spring migration and the direction of natal dispersal. In contrast, adult redstarts showed considerable site fidelity between breeding seasons, indicating that environmental conditions did not affect dispersal patterns after the first breeding attempt. Our findings suggest that habitat occupancy during the first nonbreeding season helps determine the latitude at which this species of Neotropical–Nearctic migratory bird breeds throughout its life and emphasize the need to understand how events throughout the annual cycle interact to shape fundamental biological processes

Planar defects as Ar traps in trioctahedral micas: A mechanism for increased Ar retentivity in phlogopite

The effects of planar defects and composition on Ar mobility in trioctahedral micas have been investigated in samples from a small marble outcrop (~500m 2) in the Frontenac Terrane, Grenville Province, Ontario. These micas crystallized during amphibolite-facies metamorphism at ~1170Ma and experienced a thermal pulse ~100Ma later at shallow crustal levels associated with the emplacement of plutons. 87Rb/ 86Sr ages of the phlogopites range from ~950 to ~1050Ma, consistent with resetting during the later thermal event. The same phlogopites however, give 40Ar/ 39Ar ages between ~950 and 1160Ma, spanning the age range of the two thermal events. This result is intriguing because these micas have undergone the same thermal history and were not deformed after peak metamorphic conditions. In order to understand this phenomenon, the chemical, crystallographical, and microstructural nature of four mica samples has been characterized in detail using a wide range of analytical techniques. The scanning electron microscope (SEM), electron microprobe (EMP), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) data show that the micas are chemically homogeneous (with the exception of Ba) and similar in composition. The Fourier transform infrared spectroscopy and Mossbauer results show that the M sites for three of the micas are dominated by divalent cations and the Fe 3+/(Fe 2++Fe 3+) ratio for all four phlogopites ranges from 0.10 to 0.25. The stable-isotopic data for calcite indicate that this outcrop was not affected by hydrothermal fluids after peak metamorphism. No correlation between chemical composition and 87Rb/ 86Sr and 40Ar/ 39Ar age or between crystal size and 40Ar/ 39Ar age is observed. The only major difference among all of the micas was revealed through transmitted electron microscope (TEM), which shows that the older 1M micas contain significantly more layer stacking defects, associated with crystallization, than the younger micas. We propose that these defect structures, which are enclosed entirely within the mineral grain may serve as Ar traps and effectively increase the Ar retentivity of the mineral. As this phenomenon has not been previously documented in micas, this may have significant implications for the interpretation of 40Ar/ 39Ar ages of minerals which have similar defect structures