Horizontal mixing of Great Barrier Reef waters: Offshore diffusivity determined from radium isotope distribution

Hancock, Gary; Webster, Ian T.; Stieglitz, Thomas

doi:10.1029/2006jc003608

Cited by 93 publications

(115 citation statements)

References 36 publications

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“…A similar calculation for the southern GBR, between 23°S and 20°S, indicates that in just 8 h, there is an exchange of water with the Pacific Ocean equal to the entire yearly river discharge for the region. It should again be noted that these calculations are based on an exchange time of 100 d, even though this work and other studies [Hancock et al, 2006;Wang et al, 2007] indicate possibly much shorter exchange times.…”

Section: Discussionmentioning

confidence: 73%

On the surface circulation in the western Coral Sea and residence times in the Great Barrier Reef

Choukroun¹,

Ridd²,

Brinkman³

et al. 2010

J. Geophys. Res.

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[1] Surface velocity observations from satellite tracked drifters made between 1987 and 2008 were used to resolve the surface circulation of the western Coral Sea, west of 158°E, and the Great Barrier Reef (GBR). The mean surface current map depicts well the major circulation patterns of the region, such as the position of the north Vanuatu and north Caledonia jets (NVJ and NCJ) and the western boundary currents. The North Queensland Current (NQC) and the East Australian Current (EAC) are well defined, flowing at speeds greater than 50 cm s −1 to the north, south of 15°S and 19°S, respectively. The NQC/EAC is mainly formed by the NVJ/NCJ flows, respectively. The presence of the Queensland Plateau greatly affects the westward flow, causing a zone of weak and highly variable currents that extends from 15°S to 18°S between the Queensland Plateau and the GBR shelf. Of the 235 drifters that crossed the western Coral Sea, 75 entered the GBR. Analysis of the drifter trajectories inside the GBR reveals the presence of a northwestward circulation at speeds of 22 cm s −1 north of 18°S and 0.5 cm s −1 south of 18°S. Drifter travel times used to evaluate the water residence times within the GBR indicate residence times of a few weeks for most of the lagoon.

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Section: Discussionmentioning

confidence: 73%

On the surface circulation in the western Coral Sea and residence times in the Great Barrier Reef

Choukroun¹,

Ridd²,

Brinkman³

et al. 2010

J. Geophys. Res.

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“…In the southern GBR, the deep (80-150 m) Capricorn Channel separates the inner and the outer shelf into two distinct reef systems, while a stable cyclonic eddy, the Capricorn Eddy, typically forms in the lee of the shelf bathymetry [15]. Estimates of water residence times for the GBR lagoon differ between recent studies, ranging from weeks [14,16,17] to several months [13,18]. Analyses of satellite imagery of riverine flood plumes suggest water residence times of several weeks in the coastal and inshore GBR [19,20].…”

Section: Introductionmentioning

confidence: 94%

Satellite-Derived Photic Depth on the Great Barrier Reef: Spatio-Temporal Patterns of Water Clarity

et al. 2012

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Detecting changes to the transparency of the water column is critical for understanding the responses of marine organisms, such as corals, to light availability. Long-term patterns in water transparency determine geographical and depth distributions, while acute reductions cause short-term stress, potentially mortality and may increase the organisms' vulnerability to other environmental stressors. Here, we investigated the optimal, operational algorithm for light attenuation through the water column across the scale of the Great Barrier Reef (GBR), Australia. We implemented and tested a quasi-analytical algorithm to determine the photic depth in GBR waters and matched regional Secchi depth (Z SD ) data to MODIS-Aqua (2002 and SeaWiFS (1997SeaWiFS ( -2010 satellite data. The results of the in situ Z SD /satellite data matchup showed a simple bias offset between the in situ and satellite retrievals. Using a Type II linear regression of log-transformed satellite and in situ data, we estimated Z SD and implemented the validated Z SD algorithm to generate a decadal satellite time series (2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) values during the austral summer, most likely due to river runoff and increased vertical mixing, and a decline in water clarity between 2008-2012, reflecting a prevailing La Niña weather pattern. The decline in water clarity was most pronounced in the inshore area, where a significant decrease in mean inner shelf Z SD of 2.1 m (from 8.3 m to 6.2 m) occurred over the decade. Empirical Orthogonal Function Analysis determined the dominance of Mode 1 (51.3%), with the greatest variation in water clarity along the mid-shelf, reflecting the strong influence of oceanic intrusions on the spatio-temporal patterns of water clarity. The newly developed photic depth product has many potential applications for the GBR from water quality monitoring to analyses of ecosystem responses to changes in water clarity.

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“…K d = Ra solid /Ra liquid Distribution coefficients are determined in a variety of ways, usually in laboratory experiments where Ra isotopes are spiked onto sediment/water slurries (Rama and Moore, 1996;Hancock et al, 2006) or in laboratory experiments where sediment and water are equilibrated (Webster et al, 1995 (Benes, 1990). It is also important to determine which fraction of the sedimentary Ra pool is being used to calculate K d .…”

Section: )mentioning

confidence: 99%

“…Ra release in surface estuaries has been mainly attributed to desorption of Ra from suspended and bottom sediments as salinity increases (Li and Chan, 1979;Elsinger and Moore, 1980). However, radium behavior within the STE has additional complexity including varying fractions of exchangeable sediment Ra (Porcelli and Swarzenski, 2003); grain size and porosity of sediments (Webster et al, 1995, Hancock et al, 2006; changes in ionic strength (salinity) (Elsinger and Moore, 1980;Webster et al, 1995); temperature effects (Rama and Moore, 1996); pH (Sanchez and Rodriguez-Alvarez, 1999;Lauria et al, 2004); and barite solubility (Ba and Ra are chemical analogs) (Langmuir and Riese, 1985;Grundl and Cape, 2006). Other controls have been suggested but not thoroughly examined including the redox state of groundwater (including Eh and pH) (Puigdomènech and Bergström, 1995;Porcelli and Swarzenski, 2003) and the presence Fe and, in particular, Mn (hydr)oxides, since Ra has a very high affinity for Mn and Fe (Bollinger and Moore, 1993;Sun and Torgersen, 2001;Charette and Sholkovitz, 2006).…”

Section: Introductionmentioning

confidence: 99%

New perspectives on radium behavior within a subterranean estuary

et al. 2008

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Abstract:Over the past decade, radium isotopes have been frequently applied as tracers of submarine groundwater discharge (SGD). The unique radium signature of SGD is acquired within the subterranean estuary, a mixing zone between fresh groundwater and seawater in coastal aquifers, yet little is known about what controls Ra cycling in this system. The focus of this study was to examine controls on sediment and groundwater radium activities within permeable aquifer sands (Waquoit Bay, MA, USA) through a combination of field and laboratory studies. In the field, a series of sediment cores and corresponding groundwater profiles were collected for analysis of the four radium isotopes, as well as dissolved and sediment associated manganese, iron, and barium. We found that in addition to greater desorption at increasing salinity, radium was also closely tied to manganese and iron redox cycling within these sediments. A series of laboratory adsorption/desorption experiments helped elucidate the importance of 1) contact time between sediment and water, 2) salinity of water in contact with sediment, 3) redox conditions of water in contact with sediment, and 4) the chemical characteristics of sediment on radium adsorption/desorption. We found that these reactions are rapid (on the order of hours), desorption increases with increasing salinity and decreasing pH, and the presence of Fe and Mn (hydr)oxides on the sediment inhibit the release of radium.These sediments have a large capacity to sorb radium from fresh water. Combined with these experimental results, we present evidence from time series groundwater sampling 2 that within this subterranean estuary there are cyclic periods of Ra accumulation and release controlled by changing salinity and redox conditions.

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Horizontal mixing of Great Barrier Reef waters: Offshore diffusivity determined from radium isotope distribution

Cited by 93 publications

References 36 publications

On the surface circulation in the western Coral Sea and residence times in the Great Barrier Reef

On the surface circulation in the western Coral Sea and residence times in the Great Barrier Reef

Satellite-Derived Photic Depth on the Great Barrier Reef: Spatio-Temporal Patterns of Water Clarity

New perspectives on radium behavior within a subterranean estuary

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