Spawning dynamics of the eastern gemfish (Rexea solandri) in relation to regional oceanography in south-eastern Australia

2001 ◽  
Vol 52 (4) ◽  
pp. 611 ◽  
Author(s):  
Jeremy D. Prince ◽  
David A. Griffin
Keyword(s):  
Continental Shelf ◽  
Winter Season ◽  
Shelf Break ◽  
Sea Surface ◽  
Mode Water ◽  
Topographic Features ◽  
Warm Core ◽  
Eastern Australia ◽  
Northern Edge ◽  
Survival And Growth

Experienced fishers believe the winter aggregations of gemfish are influenced by the following: cold bottom currents from the south and east flowing up onto the shelf; the edge of warm-core eddies; and topographic features along the shelf break. These claims were tested through observations made at sea during industry surveys of the winter gemfish seasons 1996 –98, and the study of 250 m isotherm charts, sea surface temperature data, and historic catch data. The study generally confirmed the anecdotal information collected from the fishers. The first gemfish aggregations of the winter season often form on the southern edge of a warm-core eddy. Secondarily, aggregations tend to form around the northern edge of the warm-core eddy if it is interacting with the shelf break. Finally, gemfish aggregate around the point at which the main flow of the East Australian Current (EAC) detaches from the continental shelf. This timing and location apparently coincides with conditions conducive to the production of subsurface plumes of nutrient-rich deep Sub-Antarctic mode Water. These plumes lead to seasonal enhancement of phytoplankton growth along the edge of the continental shelf, which may offer the adaptive advantage of enhancing the survival and growth of larval gemfish.

Active and passive dispersal of Centroberyx affinis (Berycidae) and Gonorynchus greyi (Gonorynchidae) larvae on the Sydney shelf

2000 ◽  
Vol 51 (3) ◽  
pp. 229 ◽  
Author(s):  
Kimberley A. Smith
Keyword(s):  
Continental Shelf ◽  
Larval Stage ◽  
Shelf Break ◽  
Outer Shelf ◽  
Size Distributions ◽  
Passive Dispersal ◽  
Larval Size ◽  
Larval Behaviour ◽  
Eastern Australia ◽  
Spawning Periods

Distributions of small and large larvae of Centroberyx affinis (Berycidae) and Gonorynchus greyi (Gonorynchidae) were examined along a shore-normal transect across the Sydney continental shelf, south-eastern Australia during January and April 1994. Both species were abundant, and 3016 individuals of C. affinis and 3184 individuals of G. greyi were taken. Distributions of small and large C. affinis reflected hydrographic variability and suggested passive dispersal. Previous observations of high year-class variability for this species may therefore reflect oceanographic variability during the larval stage. In contrast, the distributions of G. greyi only partially reflected hydrography and appeared to be influenced by larval behaviour at both sizes. Size distributions during each month indicated protracted spawning periods for both species. Spawning by C. affinis may have occurred over the inner shelf although the location was unclear because of the complexity of nearshore currents. Spawning by G. greyi probably occurred over the outer shelf. An increasing influence of larval behaviour with larval size on the distribution of G. greyi restricted larger individuals to the shelf break; this may have been a response to higher productivity in this region.

Ichthyoplankton Associated with a Warm Core Ring off the Scotiars Shelf

1984 ◽  
Vol 41 (2) ◽  
pp. 294-303 ◽  
Author(s):  
J. S. Wroblewski ◽  
Jerry Cheney
Keyword(s):  
Continental Shelf ◽  
Shelf Break ◽  
Shelf Water ◽  
Scotian Shelf ◽  
Larval Drift ◽  
Warm Core ◽  
Warm Core Ring ◽  
Shelf Slope ◽  
Continental Shelf Break ◽  
Upper Slope

A warm core ring and adjacent waters off the Scotian Shelf in June 1982 contained substantial numbers of larval and juvenile white hake, Urophycis tenuis, as far as 140 km seaward of the continental shelf break. The warm core ring, designated 81-G, had entrained shelf water on several occasions before the shipboard observations were made. We suggest that the ring contributed to the offshore advection of these fish, which probably were spawned on the continental shelf or upper slope. Warm core rings can disrupt the usual larval drift pattern of shelf–slope fishes and thereby affect recruitment. Larvae and juveniles of several species of tropical–subtropical fishes found in ring 81-G have been reported previously as rare specimens in ichthyoplankton surveys on the Scotian Shelf. Our observations support the hypothesis that warm core rings can be a mechanism for transport of these expatriated fishes onto the shelf.

Yellowfin tuna (Thunnus albacares) aggregations along the shelf break off south-eastern Australia: links between inshore and offshore processes

2001 ◽  
Vol 52 (4) ◽  
pp. 463 ◽  
Author(s):  
J. W. Young ◽  
R. Bradford ◽  
T. D. Lamb ◽  
L. A. Clementson ◽  
R. Kloser ◽  
...  
Keyword(s):  
Yellowfin Tuna ◽  
Shelf Break ◽  
Thunnus Albacares ◽  
Catch Per Unit Effort ◽  
South Eastern ◽  
Warm Core ◽  
South Wales ◽  
Eastern Australia ◽  
High Concentrations ◽  
South Eastern Australia

In May 1996 the biological oceanography of the main yellowfin tuna longline fishing waters off southern New South Wales, Australia, was examined in relation to the catch by the fishery. A warm-core eddy was identified directly east of Eden with a temperature at 250 m depth of 15˚C. At the western edge of this eddy, relatively high levels of fluorescence (chlorophyll a) were recorded together with pigments typical of diatoms, a feature of upwelling communities. The biomass of zooplankton and micronekton was also significantly higher at the western edge of the eddy. Similarly, acoustic data showed relatively high concentrations of backscatter at the margins of the eddy, particularly at the shelf break and slope. These areas had the greatest potential prey biomass; a fact supported by the presence of shelf-and slope-associated prey species in the stomachs of yellowfin tuna caught at the same time. Fishery data for yellowfin tuna (Thunnus albacares) captures showed that catch per unit effort was highest along the shelf and shelf break. Examination of yellowfin tuna catch records from 1988 to 1998 from south-eastern Australia showed highest catches in 1996, ~75%of the catch coming from the western edge of the eddy. We conclude that the presence of a warm-core eddy in the area at this time provided a localized but productive area to which the yellowfin were attracted.

scholarly journals Stability of a buoyancy-driven coastal current at the shelf break

2002 ◽  
Vol 452 ◽  
pp. 97-121 ◽  
Author(s):  
C. CENEDESE ◽  
P. F. LINDEN
Keyword(s):  
Continental Shelf ◽  
Continental Slope ◽  
Unstable Mode ◽  
Shelf Break ◽  
Coastal Current ◽  
Surface Currents ◽  
Flat Bottom ◽  
Vertical Boundary ◽  
Axisymmetric Disturbances ◽  
A Current

Buoyancy-driven surface currents were generated in the laboratory by releasing buoyant fluid from a source adjacent to a vertical boundary in a rotating container. Different bottom topographies that simulate both a continental slope and a continental ridge were introduced in the container. The topography modified the flow in comparison with the at bottom case where the current grew in width and depth until it became unstable once to non-axisymmetric disturbances. However, when topography was introduced a second instability of the buoyancy-driven current was observed. The most important parameter describing the flow is the ratio of continental shelf width W to the width L* of the current at the onset of the instability. The values of L* for the first instability, and L*−W for the second instability were not influenced by the topography and were 2–6 times the Rossby radius. Thus, the parameter describing the flow can be expressed as the ratio of the width of the continental shelf to the Rossby radius. When this ratio is larger than 2–6 the second instability was observed on the current front. A continental ridge allowed the disturbance to grow to larger amplitude with formation of eddies and fronts, while a gentle continental slope reduced the growth rate and amplitude of the most unstable mode, when compared to the continental ridge topography. When present, eddies did not separate from the main current, and remained near the shelf break. On the other hand, for the largest values of the Rossby radius the first instability was suppressed and the flow was observed to remain stable. A small but significant variation was found in the wavelength of the first instability, which was smaller for a current over topography than over a flat bottom.

scholarly journals Seasonal trends and phenology shifts in sea surface temperature on the North American northeastern continental shelf

Elem Sci Anth ◽  
2017 ◽  
Vol 5 ◽  
Author(s):  
Andrew C. Thomas ◽  
Andrew J. Pershing ◽  
Kevin D. Friedland ◽  
Janet A. Nye ◽  
Katherine E. Mills ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Continental Shelf ◽  
Sea Surface Temperature ◽  
North American ◽  
Gulf Of Maine ◽  
Sea Surface ◽  
Scotian Shelf ◽  
Seasonal Differences ◽  
Study Region ◽  
The North

The northeastern North American continental shelf from Cape Hatteras to the Scotian Shelf is a region of globally extreme positive trends in sea surface temperature (SST). Here, a 33-year (1982–2014) time series of daily satellite SST data was used to quantify and map spatial patterns in SST trends and phenology over this shelf. Strongest trends are over the Scotian Shelf (>0.6°C decade–1) and Gulf of Maine (>0.4°C decade–1) with weaker trends over the inner Mid-Atlantic Bight (~0.3°C decade–1). Winter (January–April) trends are relatively weak, and even negative in some areas; early summer (May–June) trends are positive everywhere, and later summer (July–September) trends are strongest (~1.0°C decade–1). These seasonal differences shift the phenology of many metrics of the SST cycle. The yearday on which specific temperature thresholds (8° and 12°C) are reached in spring trends earlier, most strongly over the Scotian Shelf and Gulf of Maine (~ –0.5 days year–1). Three metrics defining the warmest summer period show significant trends towards earlier summer starts, later summer ends and longer summer duration over the entire study region. Trends in start and end dates are strongest (~1 day year–1) over the Gulf of Maine and Scotian Shelf. Trends in increased summer duration are >2.0 days year–1 in parts of the Gulf of Maine. Regression analyses show that phenology trends have regionally varying links to the North Atlantic Oscillation, to local spring and summer atmospheric pressure and air temperature and to Gulf Stream position. For effective monitoring and management of dynamically heterogeneous shelf regions, the results highlight the need to quantify spatial and seasonal differences in SST trends as well as trends in SST phenology, each of which likely has implications for the ecological functioning of the shelf.

scholarly journals Upper ocean stratification and sea ice growth rates during the summer-fall transition, as revealed by Elephant seal foraging in the Adélie Depression, East Antarctica

Ocean Science ◽  
2011 ◽  
Vol 7 (2) ◽  
pp. 185-202 ◽  
Author(s):  
G. D. Williams ◽  
M. Hindell ◽  
M.-N. Houssais ◽  
T. Tamura ◽  
I. C. Field
Keyword(s):  
Sea Ice ◽  
Continental Shelf ◽  
Mixed Layer ◽  
Growth Rates ◽  
Shelf Break ◽  
Upper Ocean ◽  
Ocean Stratification ◽  
Glacier Tongue ◽  
Ice Growth ◽  
Continental Shelf Break

Abstract. Southern elephant seals (Mirounga leonina), fitted with Conductivity-Temperature-Depth sensors at Macquarie Island in January 2005 and 2010, collected unique oceanographic observations of the Adélie and George V Land continental shelf (140–148° E) during the summer-fall transition (late February through April). This is a key region of dense shelf water formation from enhanced sea ice growth/brine rejection in the local coastal polynyas. In 2005, two seals occupied the continental shelf break near the grounded icebergs at the northern end of the Mertz Glacier Tongue for several weeks from the end of February. One of the seals migrated west to the Dibble Ice Tongue, apparently utilising the Antarctic Slope Front current near the continental shelf break. In 2010, immediately after that year's calving of the Mertz Glacier Tongue, two seals migrated to the same region but penetrated much further southwest across the Adélie Depression and sampled the Commonwealth Bay polynya from March through April. Here we present observations of the regional oceanography during the summer-fall transition, in particular (i) the zonal distribution of modified Circumpolar Deep Water exchange across the shelf break, (ii) the upper ocean stratification across the Adélie Depression, including alongside iceberg C-28 that calved from the Mertz Glacier and (iii) the convective overturning of the deep remnant seasonal mixed layer in Commonwealth Bay from sea ice growth. Heat and freshwater budgets to 200–300 m are used to estimate the ocean heat content (400→50 MJ m−2), flux (50–200 W m−2 loss) and sea ice growth rates (maximum of 7.5–12.5 cm day−1). Mean seal-derived sea ice growth rates were within the range of satellite-derived estimates from 1992–2007 using ERA-Interim data. We speculate that the continuous foraging by the seals within Commonwealth Bay during the summer/fall transition was due to favorable feeding conditions resulting from the convective overturning of the deep seasonal mixed layer and chlorophyll maximum that is a reported feature of this location.

scholarly journals Statistical Downscaling Forecasts for Winter Monsoon Precipitation in Malaysia Using Multimodel Output Variables

2010 ◽  
Vol 23 (1) ◽  
pp. 17-27 ◽  
Author(s):  
Liew Juneng ◽  
Fredolin T. Tangang ◽  
Hongwen Kang ◽  
Woo-Jin Lee ◽  
Yap Kok Seng
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Statistical Downscaling ◽  
Large Scale ◽  
Winter Season ◽  
Peninsular Malaysia ◽  
Sea Surface ◽  
Asia Pacific ◽  
Forecast Data ◽  
Multimodel Ensembles

Abstract This paper compares the skills of four different forecasting approaches in predicting the 1-month lead time of the Malaysian winter season precipitation. Two of the approaches are based on statistical downscaling techniques of multimodel ensembles (MME). The third one is the ensemble of raw GCM forecast without any downscaling, whereas the fourth approach, which provides a baseline comparison, is a purely statistical forecast based solely on the preceding sea surface temperature anomaly. The first multimodel statistical downscaling method was developed by the Asia-Pacific Economic Cooperation (APEC) Climate Center (APCC) team, whereas the second is based on the canonical correlation analysis (CCA) technique using the same predictor variables. For the multimodel downscaling ensemble, eight variables from seven operational GCMs are used as predictors with the hindcast forecast data spanning a period of 21 yr from 1983/84 to 2003/04. The raw GCM forecast ensemble tends to have higher skills than the baseline skills of the purely statistical forecast that relates the dominant modes of observed sea surface temperature variability to precipitation. However, the downscaled MME forecasts have higher skills than the raw GCM products. In particular, the model developed by APCC showed significant improvement over the peninsular Malaysia region. This is attributed to the model’s ability to capture regional and large-scale predictor signatures from which the additional skills originated. Overall, the results showed that the appropriate downscaling technique and ensemble of various GCM forecasts could result in some skill enhancement, particularly over peninsular Malaysia, where other models tend to have lower or no skills.

scholarly journals Modelling a tropical-like cyclone in the Mediterranean Sea under present and warmer climate

2021 ◽  
Vol 21 (1) ◽  
pp. 53-71
Author(s):  
Shunya Koseki ◽  
Priscilla A. Mooney ◽  
William Cabos ◽  
Miguel Ángel Gaertner ◽  
Alba de la Vara ◽  
...  
Keyword(s):  
Climate Change ◽  
Global Warming ◽  
Water Vapour ◽  
Surface Wind ◽  
Sea Surface ◽  
Future Climate Change ◽  
Cumulus Convection ◽  
Present Climate ◽  
Prognostic Variables ◽  
Warm Core

Abstract. This study focuses on a single Mediterranean hurricane (hereafter medicane), to investigate its response to global warming during the middle of the 21st century and assesses the effects of a warmer ocean and a warmer atmosphere on its development. Our investigation uses the state-of-the-art regional climate model WRF to produce the six-member, multi-physics ensembles. Results show that our model setup simulates a realistic cyclone track and the transition from an initial disturbance to a tropical-like cyclone with a deep warm core. However, the simulated transition occurs earlier than for the observed medicane. The response of the medicane to future climate change is investigated with a pseudo global warming (PGW) approach. This is the first application of the PGW framework to medicanes. The PGW approach adds a climate change delta (defined as difference between future and present climate) to WRF's boundary conditions which is obtained for all prognostic variables using the mean change in an ensemble of CMIP5 simulations. A PGW simulation where the climate change delta is added to all prognostic variables (PGWALL) shows that most of the medicane characteristics moderately intensify, e.g. surface wind speed, uptake of water vapour, and precipitation. However, the minimum sea level pressure (SLP) is almost identical to that under present climate conditions. Two additional PGW simulations were undertaken; One simulation adds the projected change in sea surface and skin temperature only (PGWSST) while the second simulation adds the PGW changes to only atmospheric variables (PGWATMS); i.e. we use present-day sea surface temperatures. These simulations show opposing responses of the medicane. In PGWSST, the medicane is more intense than PGWALL as indicated by lower SLP values, the stronger surface wind, and the more intense evaporation and precipitation. In contrast, the medicane in PGWATMS still transitions into a tropical-like cyclone with a deep warm core, but the PGWATMS medicane weakens considerably (SLP, surface wind, and rainfall decrease). This difference can be explained by an increase in water vapour driven by the warmer ocean surface (favourable for cumulus convection). The warmer and drier atmosphere in PGWATMS tends to inhibit condensation (unfavourable for cumulus convection). The warmer ocean and warmer atmosphere have counteracting effects which leads to only a modest enhancement of the medicane by global warming. The novel approach in this study provides new insights into the different roles of warming of the ocean and atmosphere in medicane development.

Mesoscale, tidal and seasonal/interannual drivers of the Weddell Sea overturning circulation

2021 ◽  
Keyword(s):  
Continental Shelf ◽  
Shelf Break ◽  
Weddell Sea ◽  
Global Ocean ◽  
Mean Flow ◽  
Ice Shelf ◽  
Overturning Circulation ◽  
Global Circulation ◽  
Interannual Fluctuations ◽  
Continental Shelf Break

Abstract The Weddell Sea supplies 40–50% of the Antarctic BottomWaters that fill the global ocean abyss, and therefore exerts significant influence over global circulation and climate. Previous studies have identified a range of different processes that may contribute to dense shelf water (DSW) formation and export on the southern Weddell Sea continental shelf. However, the relative importance of these processes has not been quantified, which hampers prioritization of observational deployments and development of model parameterizations in this region. In this study a high-resolution (1/12°) regional model of the southern Weddell Sea is used to quantify the overturning circulation and decompose it into contributions due to multi-annual mean flows, seasonal/interannual variability, tides, and other sub-monthly variability. It is shown that tides primarily influence the overturning by changing the melt rate of the Filchner-Ronne Ice Shelf (FRIS). The resulting ~0.2 Sv decrease in DSW transport is comparable to the magnitude of the overturning in the FRIS cavity, but small compared to DSW export across the continental shelf break. Seasonal/interannual fluctuations exert a modest influence on the overturning circulation due to the relatively short (8-year) analysis period. Analysis of the transient energy budget indicates that the non-tidal, sub-monthly variability is primarily baroclinically-generated eddies associated with dense overflows. These eddies play a comparable role to the mean flow in exporting dense shelf waters across the continental shelf break, and account for 100% of the transfer of heat onto the continental shelf. The eddy component of the overturning is sensitive to model resolution, decreasing by a factor of ~2 as the horizontal grid spacing is refined from 1/3° to 1/12°.

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