Methodologies Sampling Trace-metal clean samples: Samples for trace element determinations, and for culture work were obtained using a Go-Flo bottles mounted on a polyurethane-coated rosette frame containing a SeaBird SBE 911 ctd, an SBE 43 DO dissolved oxygen sensor and a Wet Labs ECO-AFL Flourometer. The package was lowered using a polyurethane coated 4-conductor Kevlar cable and individual bottles were fired using the SBE seasoft computer program. Water samples were obtained during the upcast and bottles were tripped while the package was still moving slowly (510 m/min) upwards into clean water. As soon as the package was recovered the Go-Flo bottles were removed from the rosette frame and brought into the TM clean van within which a Mac-10 HEPA unit and a ENVIRCO class 100 laminar flow hood were operated constantly to remove particulates from the air. Unfiltered samples were collected for salinity, nutrients etc. to establish the integrity of the samples. For filtered samples the Go-Flo bottles were pressurised using filtered compressed air to <10 psi and the water passed though 0.45 um Supor membrane polysulfone filters which had previously been acid washed and rinsed in DI water. After sub-sampling the filters were washed in DI water, dried and returned to shore for determination of particulate loads. Shipboard trace metal determinations Total Dissolved Iron Analysis: Dissolved Fe was determined using the Flow Injection Analysis (FIA) scheme (Measures et al., 1995). The pre-concentration column used for this determination was found to bleed an unacceptably high level of Fe into the system and was replaced after station ?? with a ~ 1m injection loop. While the substitution eliminated the blank problem the sensitivity of the method was reduced by ~ 10-fold. The minimal detectable quantity using the injection loop was approximatley 60-150 pM. Precision was typically 1.8% at 1 nM Shore-based Total Dissolved Fe Analysis: The accuracy of the shipboard dissolved Fe analyses will be assessed by the analysis of replicate subsamples (stored acidified to 0.024M Q-HCl) from selected depths in each profile using the Fe-57 isotope dilution method of Wu and Boyle(1998). These determinations will be carried out by W.M. Landing at FSU using high-resolution (HR-ICPMS) analysis with a Finnegan Element I high-resolution magnetic sector ICPMS. Landing has a precision of 3-6% for replicate determinations using this techniques, and is also participating in the SCOR-sponsored dissolved Fe inter-comparison study. It is expected that this phase of the work will be accomplished by December. Total Dissolved Aluminium Analysis: The Flow Injection Analysis (FIA) method of Resing and Measures (1994) was used to determine Al concentrations. This fluorometric method (based on Hydes and Liss, 1976), using a 1-minute pre-concentration had a detection limit of ~0.4 nM and a precision of 2.7% at 3 nM. Total Dissolved Manganese Analysis: The FIA method (Resing and Mottl, 1992) was used to determine total dissolved Mn. The method, was used with a 1-minute pre-concentration and had a detection limit of 50-100 pM and a precision of 8% at 0.5 nM. Particulate material: Total particulate Fe, Al and Mn will be determined by analysis of material collected onto preweighed 0.2µm filters. The filters will be digested using HNO3 in Teflon bombs using a microwave digestion system. The digest will be analysed using the FIA systems outlined above. Due to equipment deployment requirements for other NSF projects, the results of this work are not expected until late Spring 2005. Shipboard results and interpretation A total of 450 samples were collected at 36 stations. Shipboard dissolved Fe, Al and Mn are reported. Each sample is reported with a quality flag to indicate the reliability of the data. At this stage the data set the only quality flag assigned to samples is 8 to indicate samples that were obtained from Go-Flo bottles that were suspected of pre or post-tripping. These samples were identified by a mismatch between the in situ salinity recorded by the SBE 911 ctd and the discrete salinity sample collected from the Go-Flo rosette during the subsampling operation. At this stage comparison between discrete salinity data and ctd records has only reached Station 48. Thus samples with higher station numbers than this may also contain erroneous data from pre or post-tripped bottles. Run with pre-concentration column Station 3 Station 16 Station 19 –currently not blank corrected 0.69 nM Fe blank correction applied 0.55 nM Fe blank correction applied Run with injection loop All others Interpretation Drake Passage Dissolved Fe values ranged by two orders of magnitude from 0.050 to 5.46 nM, dissolved Al varied 15 fold from 0.48 to 7.6 nM and Mn varied by more than 200fold from 0.04 to 9 nM. The systematics of the trace metal distributions can be envisaged as being the result of the addition of large amounts of these trace metals to very low background source water followed by the biological modification of that water. Addition of the trace metals appears to result from the impingement of the ACC water onto the shelf at the region of the Shackleton fracture zone. Lowest concentrations for all three dissolved trace elements were found associated with the "blue water" regions as represented by stations upstream, or close to the Shackleton FZ e.g.16b, 29b, 55a/g, 70c. In addition low concentrations for all metals were observed at offshore stations in the NE quadrant of the station grid, e.g. 42e, 64g and 68a. In contrast, the highest values were found for all three elements in the coastal shelf stations e.g. 3a, 19a, 57e, 58c, Or in the water advected off the shelf into the NE quadrant of the sampling grid, e.g. 31a, 33a, 66c. Intermediate values, i.e. high concentrations of Mn, a tracer of shelf addition, but low values of Fe were found at stations 36a,39a, 46a,48b,54c, 61a, 63c, 71b, 73a, 75a, 76b. These stations are presumed to represent the downstream biogeochemical modification of the enriched shelf waters where Fe has been removed from the dissolved phase into the particulate phytoplankton phase. The shape of the Mn profile appears to vary between regions of the sampling grid. For example stations 19a, 73a,75a,76b,33a and 36a all display a mid depth Mn maxima around 60-80 m, with lower values above and below. In contrast, several stations clustered together (48b,46a,54c,53a) show high Mn surface waters (1.5-4 nM) but with much lower values (<0.5nM) below 60m. The profile shapes may indicate advective outflow from different shelf regions. A third kind of profile shows uniformly high Mn in the upper water column, examples of this kind of station are 57e,58c, 31a, 66c, 39a. In these cases the water column appears to composed of a large mass of vertically mixed shelf water that has advected offshore. The inner shelf stations in this group (57e, 58c have uniformly high Fe concentrations (1-2 nM) which erode somewhat in the more offshore station 31a to 1- 1.5 nM, to the most offshore station 66c where upper water Fe has dropped to <0.5 nM despite persistently high Mn. At a larger scale it can be seen that in the Drake Passage stations Fe concentrations correlate well with both Al (figure 1; R= 0.73) and Mn (figure 2; R= 0.63) Bransfield Strait and Deception Island A total of four stations were occupied in the Bransfield strait, 2 in an offshore transect and 2 in an along strait transect , and a single station was occupied in the caldera of Deception Island. In the offshore transect the most elevated trace metals were found in the inshore station (86a), where Mn levels were 8-10 nM from 60 m to 120m, Fe values reached ~ 5nM over the same depth range and Al values were also enhanced over this depth range at~ 3 nM. The attenuation of this signal in the offshore station (89d) indicated a shelf origin for the trace elements in the Strait. Little is seen in the way of trace metal gradients along the strait (stations 94a and 95a) although a deep water (900m) maximum was seen in all metals at stn 94a, immediately downstream of a potential hydrothermal source. Within Deception Island caldera, trace metal values were extremely enriched. Mn which was uniform in the upper 80m showed a maximum of almost 200nM in the bottom waters below 110m. Fe showed a layer of uniform values (~20 nM) in the upper 50m (approximately equal to the sill depth of the caldera), declining to ~ 5 nM in deep waters. Al was fairly uniflrm at ~ 3 nM throughout the water column. While the bottom water Mn is likely a result of hydrothermal input to the bottom of the caldera, the relatively low levels of Fe at the same depth are puzzling.