Primary production in the Sub-Antarctic and Polar Frontal Zones south of Tasmania, Australia; SAZ-Sense survey, 2007

Westwood, Karen J.; Griffiths, F. Brian; Webb, Jason P.; Wright, Simon W.

doi:10.1016/j.dsr2.2011.05.017

Cited by 56 publications

(64 citation statements)

References 78 publications

(74 reference statements)

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“…At the PFZ site P2 a deep chlorophyll maximum occurred just below the euphotic depth but above the mixed layer (compare Table 1, Fig. 2 and Westwood et al, 2011) and was characterised mainly of heavily silicified diatoms and nanoflagellates (de Salas et al, 2011). Bacterial and viral abundances were higher in the SAZ than the PFZ and highest at P3 (Evans et al, 2011).…”

Section: Study Areamentioning

confidence: 94%

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Controls on mesopelagic particle fluxes in the Sub-Antarctic and Polar Frontal Zones in the Southern Ocean south of Australia in summer—Perspectives from free-drifting sediment traps

Ebersbach

Trull

Davies

et al. 2011

Deep Sea Research Part II: Topical Studies in Oceanography

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a b s t r a c tThe SAZ-Sense project examined ecosystem controls on Southern Ocean carbon export during austral summer (January-February 2007) at three locations: P1 in the low biomass Subantarctic Zone (SAZ) west of Tasmania, P3 in a region of elevated biomass in the SAZ east of Tasmania fuelled by enhanced iron supply, and P2 in High-Nutrient/Low Chlorophyll (HNLC) Polar Frontal Zone (PFZ) waters south of P1 and P3. Sinking particles were collected using (i) a cylindrical time-series (PPS3/3) trap for bulk geochemical fluxes, (ii) indented rotating sphere (IRS) traps operated as in-situ settling columns to determine the flux distribution across sinking-rate fractions, and (iii) cylindrical traps filled with polyacrylamide gels to obtain intact particles for image analysis.Particulate organic carbon (POC) flux at 150 m (PPS3/3 trap) was highest at P1, lower at P2, and lowest at P3 (3.3 71.8, 2.1 7 0.9, and 0.9 70.4 mmol m À 2 d À 1 , respectively). Biogenic silica (BSi) flux was very low in the SAZ (0.2 7 0.2 and 0.02 7 0.005 mmol m À 2 d À 1 at P1 and P3, respectively) and much higher in the PFZ (2.3 7 0.5 mmol m À 2 d À 1 at P2). Hence, the high biomass site P3 did not exhibit a correspondingly high flux of either POC or BSi. Separation of sinking-rate fractions with the IRS traps (at 170 and 320 m depth) was only successful at the PFZ site P2, where a relatively uniform distribution of flux was observed with $ 1/3 of the POC sinking faster than 100 m d À 1 and 1/3 sinking slower than 10 m d À 1 .Analysis of thousands of particles collected with the gel traps (at 140, 190, 240, and 290 m depth) enabled us to identify 5 different categories: fluff-aggregates (low-density porous or amorphous aggregates), faecal-aggregates (denser aggregates composed of different types of particles), cylindrical and ovoid faecal pellets, and isolated phyto-cells (chains and single cells). Faecal-aggregates dominated the flux at all sites, and were larger in size at P1 in comparison to P3. The PFZ site P2 differed strongly from both SAZ sites in having a much higher abundance of diatoms and relatively small-sized faecalaggregates. Overall, the particle images suggest that grazing was an important influence on vertical export at all three sites, with differences in the extents of large aggregate formation and direct diatom export further influencing the differences among the sites.

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Section: Study Areamentioning

confidence: 94%

“…Primary production estimated from tracer incubation experiments exhibited strong variability at site P1 and similar values to P3, with somewhat lower values at the PFZ Table 1 Water column properties at the process stations. Westwood et al (2011). 3.…”

Section: Study Areamentioning

confidence: 99%

Controls on mesopelagic particle fluxes in the Sub-Antarctic and Polar Frontal Zones in the Southern Ocean south of Australia in summer—Perspectives from free-drifting sediment traps

Ebersbach

Trull

Davies

et al. 2011

Deep Sea Research Part II: Topical Studies in Oceanography

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“…In the PFZ, non-limiting silicate concentrations occurred just below the euphotic depth (65 to 85 m), with a deep chlorophyll maximum (DCM) occurring just above the euphotic depth but below the mixed layer (Westwood et al, 2011). Unpublished data (B. Griffiths and B. Tilbrook, 2010) showed that silicate in surface waters was >10 µM during spring, but had been drawn down to limiting concentrations by the time of sampling in summer.…”

Section: Description Of the Region Under Studymentioning

confidence: 99%

“…See Westwood et al (2011) for a more detailed description of the GPP measurements performed during SAZ Sense. Six depths were sampled per CTD station ranging from the surface to 125 m. Sub-samples for each depth were then incubated with NaH 14 CO 3 for 1 h at 21 light intensities ranging from 0 to 416 µmol m −2 s −1 (CT Blue filter centered on 435 nm) in a temperature-controlled unit.…”

Section: Ancillary Measurementsmentioning

confidence: 99%

The influence of iron and light on net community production in the Subantarctic and Polar Frontal Zones

et al. 2011

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The roles of iron and light in controlling biomass and primary productivity are clearly established in the Southern Ocean. However, their influence on net community production (NCP) and carbon export remains to be quantified. To improve our understanding of NCP and carbon export production in the Subantarctic Zone (SAZ) and the northern reaches of the Polar Frontal Zone (PFZ), we conducted continuous onboard determinations of NCP as part of the Sub-Antarctic Sensitivity to Environmental Change (SAZ-Sense) study, which occurred in January–February 2007. Biological O2 supersaturation was derived from measuring O2/Ar ratios by equilibrator inlet mass spectrometry. Based on these continuous measurements, NCP during the austral summer 2007 in the Australian SAZ was approximately 43 mmol O2 m−2 d−1. NCP showed significant spatial variability, with larger values near the Subtropical front, and a general southward decrease. For shallower mixed layers (<50 m), dissolved Fe concentrations and Fe sufficiency, estimated from variable fluorescence, correlated strongly with NCP. The strong correlation between NCP and dissolved Fe may be difficult to interpret because of the correlation of dissolved Fe to MLD and because the concentration of iron may not be a good indicator of its availability. At stations with deeper mixed layers, NCP was consistently low, regardless of iron sufficiency, consistent with light availability also being an important control of NCP. Our new observations provide independent evidence for the critical roles of iron and light in mediating carbon export from the Southern Ocean mixed layer

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“…where J max is the maximum phytoplankton growth at a given T , assuming no light or nutrient limitation; J (z, t, T ) is the impact of light on growth rate, and is based on Westwood et al (2011), PAR is the photosynthetically available radiation, I (0, t) is the time-varying incident solar radiation at the surface, and Frac(z) is the light attenuation that is obtained from a single exponential decay law, with penetration depths based on SeaWiFS Kd-490 (which was the same as the value used by the Chen et al (1994) mixing scheme). Equation (B2) describes the zooplankton, represented as the balance between growth due to phytoplankton grazing (G(P, Z)) and losses due to zooplankton excretions (γ 2 Z) and mortality (µ Z Z 2 ).…”

Section: Appendix B Wombatmentioning

confidence: 99%

Evaluation of a near-global eddy-resolving ocean model

et al. 2013

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Abstract. Analysis of the variability of the last 18 yr (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) of a 32 yr run of a new near-global, eddy-resolving ocean general circulation model coupled with biogeochemistry is presented. Comparisons between modelled and observed mean sea level (MSL), mixed layer depth (MLD), sea level anomaly (SLA), sea surface temperature (SST), and chlorophyll a indicate that the model variability is realistic. We find some systematic errors in the modelled MLD, with the model generally deeper than observations, which results in errors in the chlorophyll a, owing to the strong biophysical coupling. We evaluate several other metrics in the model, including the zonally averaged seasonal cycle of SST, meridional overturning, volume transports through key straits and passages, zonally averaged temperature and salinity, and El Niño-related SST indices. We find that the modelled seasonal cycle in SST is 0.5-1.5 • C weaker than observed; volume transports of the Antarctic Circumpolar Current, the East Australian Current, and Indonesian Throughflow are in good agreement with observational estimates; and the correlation between the modelled and observed NINO SST indices exceeds 0.91. Most aspects of the model circulation are realistic. We conclude that the model output is suitable for broader analysis to better understand upper ocean dynamics and ocean variability at mid-and low latitudes. The new model is intended to underpin a future version of Australia's operational short-range ocean forecasting system.

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Primary production in the Sub-Antarctic and Polar Frontal Zones south of Tasmania, Australia; SAZ-Sense survey, 2007

Cited by 56 publications

References 78 publications

Controls on mesopelagic particle fluxes in the Sub-Antarctic and Polar Frontal Zones in the Southern Ocean south of Australia in summer—Perspectives from free-drifting sediment traps

Controls on mesopelagic particle fluxes in the Sub-Antarctic and Polar Frontal Zones in the Southern Ocean south of Australia in summer—Perspectives from free-drifting sediment traps

The influence of iron and light on net community production in the Subantarctic and Polar Frontal Zones

Evaluation of a near-global eddy-resolving ocean model

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