Wind and tidal mixing controls on stratification and dense water outflows in a large hypersaline bay

Hetzel, Yasha; Pattiaratchi, Charitha; Lowe, Ryan J.; Hofmeister, Richard

doi:10.1002/2015jc010733

Cited by 25 publications

(26 citation statements)

References 45 publications

(62 reference statements)

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“…This was 2-3 times stronger than the intermittent outflow measured in June/July 2009 in Naturaliste Channel [17]. This finding is consistent with the stronger Shark Bay outflow through the northern entrance proposed by James et al [14] that was based on sediment and hydrographic samples offshore, as well as descriptions based on numerical modeling [19,41]. Woo et al [15] also measured a higher salinity signature near the northern entrance as compared to the western entrance.…”

Section: Discussionsupporting

confidence: 79%

“…The deeper Geographe Channel would favour stratification, thereby encouraging the enhanced outflow. For periods of high (southerly) winds when much of the Bay becomes vertically mixed, the outflow is likely dominated by barotropic wind-driven forces [19]. Separating the baroclinic and barotropic components is difficult, but the persistence of vertical stratification and bottom outflow in Geographe Channel regardless of tidal stage and winds suggest that the barotropic flows are superimposed on the underlying density-driven flows described above.…”

Section: Discussionmentioning

confidence: 99%

“…Unfortunately, tampering caused the ADCP frame to turn upside-down after six days, requiring us to discard the last three days of data. The mooring location (4 km east of Bernier Island in 28 m water depth) was chosen based on numerical model simulations [19] showing the pathway of the dense water outflow through Geographe Channel, and for the shelter from ocean waves provided by Bernier Island. The ADCP sampled continuously in 0.5 m bins every 1-second (1 Hz) using Mode 12 with 4 sub-ping ensemble averages.…”

Section: Field Experimentsmentioning

confidence: 99%

“…Subsequent numerical modeling experiments [19] indicated that outflows through the two main channels responded differently to wind and tidal forcing, with predominance of outflow through the deeper northern entrance channel that could persist through all stages of the tide. This contrasted with observed outflows in the western channel that were more intermittent, with a stronger tidal component.…”

Section: Introductionmentioning

confidence: 99%

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Exchange Flow Variability between Hypersaline Shark Bay and the Ocean

Hetzel¹,

Pattiaratchi²,

Mihanović

2018

Preprint

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Abstract:In Shark Bay, a large hypersaline bay in Western Australia, longitudinal density gradients force gravitational circulation that is important for Bay-ocean exchange. Observations of vertical stratification and velocity are presented, confirming a steady nearbed dense water outflow from Shark Bay's northern Geographe Channel that persisted through all stages of the tide. Outflow velocities were 2-3 times stronger than the outflows recorded previously in Naturaliste Channel (in the west) and were more resistant to breakdown by tidal mixing. Estimates of turbulent kinetic energy production derived from ADCP data using the variance method showed a more complex structure in Geographe Channel, due to shear associated with the stratified conditions, with peak levels of turbulence occurring during reversal of tidal flows. For both channels the main source of turbulence was tidal flow along the seabed, with the bottom current speed cubed, |Ub 3 |, providing a reasonable proxy for tidal mixing and prediction of dense water outflows from Shark Bay the majority of the time. Orientation and deeper water of Geographe Channel along the main axis of the longitudinal density gradient provided an explanation for the predominant outflow from the Bay's northern entrance. These density-driven currents could potentially influence recruitment of commercially fished scallops and prawns through dispersal and flushing of larvae.

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Section: Discussionsupporting

confidence: 79%

Section: Discussionmentioning

confidence: 99%

Section: Field Experimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Exchange Flow Variability between Hypersaline Shark Bay and the Ocean

Hetzel¹,

Pattiaratchi²,

Mihanović

2018

Preprint

Self Cite

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show abstract

“…1) for an optimal representation of alongand across-shore processes. Similar gridding strategies were applied successfully in other coastal setups with the GETM model (Hofmeister et al, 2013;Hetzel et al, 2015). We employed integration time steps of 5 and 360 s for the 2-D and 3-D processes, respectively.…”

Section: Hydrodynamic Model and Model Couplingmentioning

confidence: 99%

The acclimative biogeochemical model of the southern North Sea

Kerimoglu¹,

Hofmeister²,

Maerz³

et al. 2017

Biogeosciences

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Abstract. Ecosystem models often rely on heuristic descriptions of autotrophic growth that fail to reproduce various stationary and dynamic states of phytoplankton cellular composition observed in laboratory experiments. Here, we present the integration of an advanced phytoplankton growth model within a coupled three-dimensional physicalbiogeochemical model and the application of the model system to the southern North Sea (SNS) defined on a relatively high resolution ( ∼ 1.5-4.5 km) curvilinear grid. The autotrophic growth model, recently introduced by Wirtz and Kerimoglu (2016), is based on a set of novel concepts for the allocation of internal resources and operation of cellular metabolism. The coupled model system consists of the General Estuarine Transport Model (GETM) as the hydrodynamical driver, a lower-trophic-level model and a simple sediment diagenesis model. We force the model system with realistic atmospheric and riverine fluxes, background turbidity caused by suspended particulate matter (SPM) and open ocean boundary conditions. For a simulation for the period 2000-2010, we show that the model system satisfactorily reproduces the physical and biogeochemical states of the system within the German Bight characterized by steep salinity; nutrient and chlorophyll (Chl) gradients, as inferred from comparisons against observation data from long-term monitoring stations; sparse in situ measurements; continuous transects; and satellites. The model also displays skill in capturing the formation of thin chlorophyll layers at the pycnocline, which is frequently observed within the stratified regions during summer. A sensitivity analysis reveals that the vertical distributions of phytoplankton concentrations estimated by the model can be qualitatively sensitive to the description of the light climate and dependence of sinking rates on the internal nutrient reserves. A non-acclimative (fixed-physiology) version of the model predicted entirely different vertical profiles, suggesting that accounting for physiological flexibility might be relevant for a consistent representation of the vertical distribution of phytoplankton biomass. Our results point to significant variability in the cellular chlorophyll-to-carbon ratio (Chl : C) across seasons and the coastal to offshore transition. Up to 3-fold-higher Chl : C at the coastal areas in comparison to those at the offshore areas contribute to the steepness of the chlorophyll gradient. The model also predicts much higher phytoplankton concentrations at the coastal areas in comparison to its non-acclimative equivalent. Hence, findings of this study provide evidence for the relevance of physiological flexibility, here reflected by spatial and seasonal variations in Chl : C, for a realistic description of biogeochemical fluxes, particularly in the environments displaying strong resource gradients.

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Impacts of Severe Tropical Cyclone Olwyn and the biogeomorphic response, Hamelin Pool, Shark Bay, Western Australia

Morris

Fearns

et al. 2022

The Depositional Record

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Storm disturbance and recovery of the peritidal benthic microbial ecosystem occurs as part of the natural climate regime in Shark Bay. However, tropical cyclone and winter storm frequency and intensity are known to be changing due to climate forcing. Presented here is an analysis of the biogeomorphic response of the benthic microbial ecosystem within the intertidal to upper subtidal zone and the beach face coquina deposits of Hamelin Pool, to the passage of Category 3 Severe Tropical Cyclone Olwyn (13 March 2015). Storm effects (initial response to 40 days post‐event) include: erosional sculpting of sediments, mats and structures; deposition and winnowing of sediments; accumulation of mucilaginous products into flocs, slurries and sludges; along with limited development of new coquina deposits in the beach face. Medium (15 months) term observations include: mat recovery and changes with transformation of mucilage deposits into new subtidal gelatinous mats, intertidal transitional mats and low‐elevation microbial structures. Observations suggest that this disturbance had both positive (the floc‐to‐mat biogeomorphic storm response) and negative feedbacks (enhanced bioturbation), which impact the development of stromatolite forming microbial mats and microbialite structures.

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Wind and tidal mixing controls on stratification and dense water outflows in a large hypersaline bay

Cited by 25 publications

References 45 publications

Exchange Flow Variability between Hypersaline Shark Bay and the Ocean

Exchange Flow Variability between Hypersaline Shark Bay and the Ocean

The acclimative biogeochemical model of the southern North Sea

Impacts of Severe Tropical Cyclone Olwyn and the biogeomorphic response, Hamelin Pool, Shark Bay, Western Australia

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