Acoustic Doppler Current Profiler measurements over the Chatham Rise

In October 2001, we observed a deep-ocean phytodetritus deposition event on Chatham Rise beneath the Subtropical Front (STF). The origin of this phytodetritus was probably an extensive phytoplankton bloom that occurred in the STF in the preceding weeks. We assessed the spatial distribution of the deposition event using video images from benthic lander and epibenthic trawl deployments and sediment pigment analyses at six sites on a north-south transect across Chatham Rise. High surficial sediment chlorophyll a concentrations were restricted spatially to the southern flank of Chatham Rise (350-1,200-m depth) with the highest values centered at ,750-m water depth (750 S). This southern 750 S site was also the only site where macroscopic phytodetritus was observed, coincident with elevated benthic biomass and sediment community respiration rates. At 750 S, phytodetritus resuspension was observed on video and corroborated by current meter, sediment trap, and optical 1 Corresponding author (s.nodder@niwa.co.nz). AcknowledgementsWe thank the officers and crew of RV Tangaroa, and numerous scientific personnel at NIOZ and NIWA, especially Henk Franken and Eilke Berghuis for lander support. Figures were drafted by Erika Mackay (NIWA). We appreciate the provision of unpublished organic carbon accumulation rates for Chatham Rise by Elisabeth Sikes (Rutgers University). We thank the SeaWiFS Project (Code 970.2) and the Distributed Active Archive Center (Code 902) at the Goddard Space Flight Center, Greenbelt, Maryland, for the production and distribution of the remotely sensed ocean color data, respectively. Thanks also to the two anonymous reviewers for their constructive comments.

Section: Discussionmentioning

confidence: 99%

Focusing of phytodetritus deposition beneath a deep‐ocean front, Chatham Rise, New Zealand

Nodder

Duineveld

Pilditch

et al. 2007

“…We simultaneously deployed duplicate arrays of free-floating sediment traps in each water mass (subtropical and subantarctic) for 48 h. The arrays were deployed approximately 5 nautical miles apart to minimize the effect of physical discontinuities, since Chiswell (1994) had observed no coherence between currents measured via moorings deployed 7 nautical miles apart on the Chatham Rise. Each array consisted of three crossframes, with the frames attached at 120 m, 300 m, and 550 m from the surface.…”

Section: Methodsmentioning

confidence: 99%

Mass sedimentation of picoplankton embedded in organic aggregates

Waite

Safi

Hall

et al. 2000

114

During a survey cruise crossing the Subtropical Front over the Chatham Rise east of New Zealand, we made the first observation in High Nutrient Low Chlorophyll waters of massive sedimentation of picoplankton embedded in large (Ͼ0.5 mm diam.) organic aggregates (OAs) sensu Riley (1963). We estimate 9.3 mg C m Ϫ2 yr Ϫ1 of prokaryotic picoplankton biomass alone may be transported below the euphotic zone via this mechanism. Using confocal microscopy, we made direct observations of picoplankton within undisrupted individual OAs, collected in sediment traps fitted with acrylimide gels, which largely conserved particle structure. Prokaryotic picoplankton autofluorescence was well-preserved and concentrations were extremely high within large rapidly sedimenting aggregates, ranging from 1.06 ϫ 10 8 ml Ϫ1 in the 120 m sediment traps in subantarctic waters to 7.5 ϫ 10 6 ml Ϫ1 at 550 m in subtropical waters, yielding Enrichment Factors of 10 3 Ϫ105 relative to picoplankton concentrations in the water column. Aggregate picoplankton concentrations showed a well-constrained exponential decline with depth, which we speculate may represent an estimate of protozoan grazing rate within the aggregates. Picoplankton were found within heterotrophic flagellates, within copepod fecal pellets, and within organic matrices, all of which were incorporated in OAs. The key event of picoplankton incorporation into initial particles occurs in the upper water column, very likely through grazing with low assimilation efficiency. Once OAs are formed, their changing porosity and reduction in picoplankton cell numbers via heterotrophy is likely to be a key factor mediating picoplankton carbon fluxes in moderately productive ecosystems, and in determining the overall particle structure of sedimenting OAs.

“…The resuspended material may be subsequently advected horizontally, probably predominantly by tidal currents (e.g. Chiswell 1994). Strong across-rise flows (up to 20 cm s-l; Chiswell 1994) are inferred to be responsible for the observed midwater increases in particle concentration on nephelometer profiles (Fig.…”

Section: Short-term Sediment Trap Fluxes From Chatham Rise Southwestmentioning

confidence: 99%

“…Meso-scale eddies could be an additional influence, especially where the East Cape Current impinges onto the northern flank of the Chatham Rise (e.g. Chiswell 1994). …”

Section: Short-term Sediment Trap Fluxes From Chatham Rise Southwestmentioning

confidence: 99%

“…The STC represents the complex mixing zone between warm (summer >15"C, winter > lO"C), highly saline (35.7-35.8%0), nutrient-poor subtropical waters to the north and cold (summer <15"C, winter < lO"C), less saline (-34.5%0), nutrient-rich subantarctic waters to the south (e.g. Heath 1985;Chiswell 1994). To the east of New Zealand, the STC is constrained bathymetrically by a broad, asymmetric submarine high, the Chatham Rise (Fig.…”

Section: Short-term Sediment Trap Fluxes From Chatham Rise Southwestmentioning

confidence: 99%

See 1 more Smart Citation

Short‐term sediment trap fluxes from Chatham Rise, southwest Pacific Ocean

Nodder

1997

Sediment trap, nephelometer, and particulate matter (PM) data were collected in the vicinity of the Subtropical Convergence, north of Chatham Rise (42–43°S), southwest Pacific Ocean, in austral autumn 1992. Free‐floating cylindrical sediment traps were deployed below the euphotic zone at 200‐, 300‐, and 500‐m water depths. Increases in total mass flux and concomitant proportional decreases in other particulate fluxes (total carbon, nitrogen, and phosphorus) with depth reflected the collection of relatively refractory material, enriched in particulate carbon, as evinced by increases in C: N and C: P ratios below 300 m. Nephelometer and PM concentration profiles indicate that resuspension of sea‐floor sediments from the nearby submarine high (Chatham Rise) probably contributed to the observed increase in total mass flux with depth. Published pCO2 estimates, biological productivity data, and moderate particulate fluxes, as indicated by the present study suggest that oceanic water types east of New Zealand may be a biologically mediated regional sink for atmospheric CO2.