Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Curation Notes
  • Problem Description
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Program Information
• Funding

Filter holders and cleaning protocol:
This was the first U.S. GEOTRACES cruise to use McLane vertical intake filter holders (https://mclanelabs.com/wp-content/uploads/2024/11/MRL-WTSLV-Filter-Holders-reference-24.K.06.pdf). This was necessitated by the at-sea loss of the previously-used "mini-MULVFS" filter holders on a prior cruise. The McLane holders are a commercial product based on the "mini-MULVFS" design that was tested and intercalibrated on the 2008 and 2009 GEOTRACES intercalibration cruises (Bishop et al. 2012) and used for all prior U.S. GEOTRACES cruises (Lam et al., 2018; Lam et al., 2015a; Xiang and Lam, 2020). The new holders retained the dimensions of the mini-MULVFS design and generally produced very good particle distributions on the filters. However, modifications in the design necessitated a change in the cleaning protocols, as the McLane version compresses 32 4"-long tubes between two plates, using an O-ring on either end of each tube for a seal. This requires a complete disassembly for cleaning prior to use. For GP17-ANT, ten McLane filter holders had difficult-to-remove red silicone O-rings embedded into a plate, which have poor resistance to HCl. Eight new McLane holders were purchased disassembled and without the embedded O-rings. For the eight new filter holders, we substituted Viton O-rings, which have much better acid-resistance. The following cleaning procedure was used:

Day 1: All disassembled components except the frit were put in a detergent bath (10% Micro) overnight. The frits were placed in a 10% TM-grade HCl bath.

Day 2: All components in detergent were rinsed thoroughly in DI water. All acid-sensitive items (silicone O-rings, components with embedded silicone O-rings, nylon wing nuts, Delrin rods, CPC quick disconnect fittings with embedded O-rings) were placed in a fresh DI bath to soak overnight to further dilute traces of detergent caught between the embedded O-rings and plates. Acid-resistant components without O-rings were placed in a 10% HCl (reagent grade) acid bath overnight. Frits soaking in 10% TM-HCl were removed, rinsed, and placed into a fresh bath of MQ water to soak.

Day 3: All components soaking overnight in 10% reagent-grade HCl from Day 2 were thoroughly rinsed with MQ water and set to dry in a laminar flow environment. Acid-sensitive fasteners (nylon wing nuts, Delrin rods, quick disconnect fittings) from Day 2 soaking in DI water were given a quick (less than 1 hour) soak in the 10% reagent-grade HCl, then rinsed thoroughly in MQ water. Acid-sensitive items that have direct contact with sample (i.e., through which seawater flows) were placed into a tub of 5% TM-grade HCl for a brief (~2 hours) soak, then removed, rinsed thoroughly in MQ water, then placed into a fresh MQ water tub to further dilute traces of acid caught between the embedded O-rings and plates. After several hours, these were given a final MQ rinse and dried under laminar flow conditions.

Frits retain acid that is not easily rinsed out, so they must be rinsed under vacuum suction: a frit was placed into a cleaned filter holder plate with its vacuum quick disconnect fitting in place, a vacuum was applied to the base of the filter holder plate while pouring MQ water onto the frit to rinse all acid out. Rinse water pH can be monitored to ensure all acid is removed. Rinsed frits should be dried in a laminar flow bench.

Day 4 or later: dried pieces can be reassembled. Frits should be packaged separately, as any residual acid fumes could degrade filter holder components in transit. Frits can take several days to dry completely. It is important that they be completely dry before packaging, as there can be mold growth on them otherwise.

Sampling:
Size-fractionated particles were collected using dual-flow McLane Research in-situ pumps (5 Dual Filter Large Volume Water Transfer System--WTS-LVDF and 3 modified Upright Large Volume Water Transfer System--WTS-LVUP). Filter holders were McLane vertical intake filter holders. At most of the stations on the continental shelf, one cast of up to 8 pumps and two filter holders per pump were deployed to collect samples at 8 depths throughout the water column. At stations off the shelf, up to 16-depths were sampled with two casts. The targeted depths of the wire-out were corrected using pressure readings from a self-recording Seabird 19plus CTD at the end of the line. One filter holder/flowpath was loaded with a Sefar polyester mesh prefilter (51 micrometers (μm) pore size, called the "Qp" filter) and paired Whatman QMA quartz fiber filters (1 μm pore size) in series ("QMA-side"). The other filter holder/flowpath was also loaded with a 51 μm prefilter (called the "Sp" filter), but it was followed by paired 0.8 μm Pall Supor800 polyethersulfone filters ("Supor-side"). A 150 μm Sefar polyester mesh was placed underneath all 51 μm prefilters and QMA filters as a support to facilitate filter handling but not analyzed. All filters and filter holders were acid-leached before use based on the recommended methods in the GEOTRACES sample and sample-handling protocols Cutter et al., 2010). QMA filters were pre-combusted at 450 degrees Celsius (°C) for 4 hours after acid leaching.

A special plate was manufactured for one of the pumps that could hold two additional McLane filter holders that were loaded with full filter sets but not connected to plumbing. These 'dipped blank' filters included the full filter sets (51 µm prefilter on top of paired QMA or paired Supor filters) with a 0.2 µm Supor polyethersulfone filter on top of the 51 µm polyester prefilters to exclude all particles from the main filter set. These were processed identically to the regular filters and functioned as full process blanks. A total of 49 dipped blank filters were used for blank subtraction, calculations of uncertainties, and determination of detection limits (Table 2).

In this dataset, data reported from the 51 μm prefilter are referred to with an "LPT" suffix to indicate large particulate total concentrations (>51 μm). Samples could come from the QMA side ("Qp" filter) or the Supor side ("Sp" filter) and are treated equivalently. Data reported from the main filters (QMA—1-51 μm —or Supor—0.8-51 μm) are from the top filter of the pair only, and are referred to with an "SPT" suffix to indicate the small particulate total concentrations.

Analytical Procedures:

Particulate organic carbon (POC) and particulate nitrogen (PN):
For SPT particles, a 25-millimeter (mm) punch of QMA filter was dried at 55°C at sea. LPT (>51 µm) particles were rinsed at sea from the Sp filter using 0.2 µm-filtered seawater onto a 25 mm 0.8 µm Ag filter (Sterlitech) and dried at 55°C at sea. These samples were beta counted for ²³⁴Th at sea by the CafeTh lab at WHOI, then sent to the Lam lab at UCSC for POC and PN analyses. POC and PN sample processing was similar to what was described in Xiang and Lam (2020). Filter samples were dismounted from the beta mounts. Typically, a 22 mm QMA subpunch or the entire 25 mm 0.8 µm Ag filter were fumed in a desiccator with concentrated HCl and dried in the oven at 60 °C overnight, and then pelletized with 30 mm tin discs from EA Consumables. Tin disc encapsulated samples were measured using a Costech 4010 Elemental Analyzer (EA) or ThermoFisher FlashEACE Instruments NC 2500 model Carbon/Nitrogen Analyzer interfaced to a Delta V Plus Continuous Flow Isotope Ratio Mass Spectrometer (IRMS) at the Stable Isotope Ecosystems Laboratory at the University of California, Merced. C and N concentrations and isotopic compositions were calibrated using the USGS 40 and USGS 41a and EA acetanilide (C8H9NO) reference materials. The isotopic data are expressed in the standard delta notation as per mil deviations (‰) with respect to international standards of Pee Dee Belemnite (PDB) and atmospheric nitrogen. The precision of the internal standard (Pugel) analyzed along with the samples in the run is 0.02‰ for d13C and 0.06‰ for d15N.

Particulate inorganic carbon (PIC):
A UIC Carbon dioxide coulometer at the UCSC Marine Analytical Lab was used for PIC measurement (Xiang and Lam, 2020). Briefly, PIC on SPT QMA punches or 1/16 LPT QMA-side prefilter was converted to CO₂ by addition of 2 N sulfuric acid. CO₂ produced is carried by a gas stream into a coulometer cell where CO₂ is quantitatively absorbed by a cathode solution, reacted to form a titratable acid and measured based on the change in current.

Biogenic silica (bSi):
A 1-hour alkaline leach with 0.2 M NaOH at 85°C was used to leach bSi for both size fractions as described in Xiang and Lam (2020) prior to the measurement on a SEAL Analytical 5-channel AA500 segmented flow nutrient analyzer at the UCSC Marine Analytical Lab.

Particulate trace metals (pTM):
pTM leachable concentrations (SPL): A 1/16ᵗʰ slice of Supor filter was leached using the "Berger Leach", a weak acid leach comprising 25%(v/v) Q-grade acetic acid and 0.02M reagent grade hydroxylamine hydrochloride (Berger et al. 2008). Samples are submerged in 2 milliliters (mL) of Berger Leach solution and heated in a 95°C water bath for 10 minutes, cooled at room temperature for about 1.3 hours, and then centrifuged for 30 minutes at 4100 rpm. Total leach time was 2 hours. 1.5 mL of the supernatant was transferred to a 15 mL Savillex vial and dried for over an hour at 110°C. The residue was redissolved and dried in concentrated HNO3 twice and brought up in 5% HNO3 spiked with 1 ppb In. Two certified reference materials (BCR-414 and PACS-2) were leached routinely alongside the samples to assure the quality of each leach (Table 1).

Analysis by ICP-MS: Sample solutions were analyzed using an Element XR high-resolution ICP-MS (Thermo Scientific) at the UCSC Plasma Analytical Facility. Elemental concentrations were standardized using multi-element, external standard curves prepared from NIST atomic absorption-standards in 5% HNO₃. Instrument drift and matrix effects were corrected using the internal 1ppb In standard and monitored using a mixed element run standard. Concentrations were determined using external standard curves of mixed trace elements standards. If a parameter was measured on the ICP-MS, the isotope and resolution (LR=Low Resolution; MR=Medium Resolution) used for the concentration measurement are indicated in Table 2.

Derived parameters:

SPM (PARTICLEMASS):
Direct comparisons between gravimetric and chemical dry weight have been made in the equatorial Atlantic, and they were found to be quite similar to each other (Bishop et al., 1977). The chemical dry weight is used to estimate SPM for each size fraction in this paper, as the sum of all major particle composition, which is the sum of POM, CaCO₃, opal, lithogenic material (Litho), and Fe and Mn (oxyhydr)oxides.

SPM [μg/L] = POM [μg/L] + CaCO₃ [μg/L] + OPAL [μg/L] + LITHO [μg/L]

+ Fe(OH)₃ [μg/L] + MnO₂ [μg/L]

Note that the resolution of this data is dictated by the lowest resolution of the component parts.

Errors in derived parameters are calculated based on rules of error propagation.

Particulate organic matter (POM):
Particulate organic matter (POM) was calculated from POC by multiplying a weight ratio of 1.88 g POM/g POC (Lam et al., 2011; Lam et al., 2017; Lam et al., 2015b), determined by Nuclear Magnetic Resonance (NMR) measurements of the phytoplankton biochemical composition (Hedges et al., 2002).

POM [μg/L] = POC [μM] × 12 [μg POC/μmol POC] × 1.88 [g POM/g POC]

Calcium carbonate (CaCO₃):
The mass concentration of CaCO₃ was calculated from PIC using a constant weight ratio:

CaCO₃ [μg/L] = PIC [μM] × 100.08 [(μg CaCO₃)/μmol PIC]

Opal:
A hydrated form of silica as SiO₂∙(0.4 H₂O) was assumed in order to calculate the mass concentrations of opal (Mortlock and Froelich, 1989):

Opal [μg/L] = bSi [μM] × 67.2 [μg opal/μmol bSi]

Lithogenic particles (Litho):
Aluminum (Al) is highly abundant in the crust and relatively invariant between two main lithogenic sources, upper continental crust (UCC Al = 8.04 wt%) and bulk continental crust (BCC Al = 8.41 wt%) (Taylor and McLennan, 1995), serving as an appropriate tracer for lithogenic particles. Total particulate Al was determined by ICP-MS after digestion (cf. Xiang and Lam 2020) and provided by our collaborator, Dr. Daniel Ohnemus, for the calculation of lithogenic particle mass. He will upload total particulate trace metals separately. Errors and quality flags for Litho_SPT and Litho_LPT will be added in the future, once Dr. Ohnemus' dataset is submitted. We assumed that most of particulate Al originates from lithogenic sources and use UCC Al wt% to calculate concentrations of lithogenic particles.

LITHO [μg/L] = Al [nmol/L] × 27×10^-3 [μg/nmol] / 0.0804 [μg Al/μg UCC]

Fe and Mn (oxy)hydroxide (Fe(OH)3 & MnO2):
For the small size fraction, these were calculated from the leachable Fe and Mn concentrations using the "Berger Leach" (Berger et al., 2008). Fe oxyhydroxides are treated as Fe(OH)₃ (ferrihydrite approximation) and Mn oxides are as MnO₂ (birnessite approximation). We apply the formula weights of 106.9 g Fe(OH)₃/mol Fe and 86.9 g MnO₂/mol Mn, respectively.

Fe(OH)₃ [μg/L] = (leachFe [nM]) × 106.9 [(ng Fe(OH)₃)/nmol Fe] × [10^-3 μg/ng]

MnO₂ [μg/L] = ( leachMn [nM] × 86.9 [(ng MnO₂)/nmol Mn] × [10^-3 μg/ng] )

For the large size fraction, where Berger Leaches were not conducted, excess Fe and Mn beyond their lithogenic contributions were assumed to be Fe and Mn (oxy)hydroxide and calculated by subtracting the lithogenic Fe and Mn from the totals. The UCC Fe/Al (0.2106) and Mn/Al (0.00367) ratios were used in the lithogenic corrections. Total particulate Al, Fe, Mn were determined by ICP-MS after digestion (cf. Xiang and Lam 2020) and provided by our collaborator, Dr. Daniel Ohnemus, for the calculation of lithogenic Al, Fe, and Mn. He will upload total particulate trace metals separately. Errors and quality flags for Fe(OH)3_LPT and MnO2_LPT will be added in the future, once Dr. Ohnemus' dataset is submitted. Fe oxyhydroxides are treated as Fe(OH)₃ (ferrihydrite approximation) and Mn oxides are as MnO₂ (birnessite approximation). We apply the formula weights of 106.9 g Fe(OH)₃/mol Fe and 86.9 g MnO₂/mol Mn, respectively. Negative numbers were set to 0.

Fe(OH)₃ [μg/L] = ( Fe [nM] - (Al [nM] × 0.2106 [nmol Fe/nmol Al]) )

×106.9 [(ng Fe(OH)₃)/nmol Fe] × [10^-3 μg/ng]

MnO₂ [μg /L] = ( Mn [nM] - (Al [nM] × 0.00367 [nmol Mn /nmol Al]) )

× 86.9 [(ng MnO₂)/nmol Mn] × [10^-3 μg/ng]

Blank subtraction:
Dipped blanks were assessed for each analyte for spatial trends, indicating potential variation in adsorption blanks, and grouped accordingly (see Table 2). Outliers for each measurement type were excluded using Chauvenet's criterion (Glover et al., 2011). The median of the appropriately grouped db filters was then used in blank subtraction to take into account the adsorption and sample handling blanks.

Dipped blank statistics can be found in Table 2.

Error propagation:
For most parameters, we could not routinely run replicates, so almost all errors reported are determined from the standard deviation of dipped blank filters (Table 2), converted to concentrations using volume filtered. This assumes that the blank subtraction is the largest source of error.

Quality flags:
All data have been assigned quality flags using the SeaDataNet Quality Flag scheme as recommended by GEOTRACES (https://www.geotraces.org/geotraces-quality-flag-policy/):

0 = no quality control (yet--forthcoming)

1 = good; passed lab QC and oceanographically consistent.

2 = possibly good; oceanographically consistent, but have minor sampling/instrumental issues.

3 = possibly bad; not oceanographically consistent, or have major sampling/instrumental issues

4 = bad; failed lab QC (including all failed pumps when only small or no volume was pumped through the filter), or known issue with samples. For a measured parameter from a failed pump, if the filter sample was analyzed and a non-zero volume was recorded so that a concentration could be derived, this concentration is reported with QF=4. These values are generally not reliable because recorded volumes for failed pumps are probably not correct. If a zero volume was recorded, then a concentration could not be derived, and the value is reported as "NaN" with QF=4. For a derived parameter from a failed pump, this QF=4 applies if any of the parameters on which it is based had a QF=4 but is not "NaN".

6 = below detection limit.

9 = data missing (including all "nd"). For a measured parameter, this QF applies to lost or missing samples that were not measured. For a derived parameter, this QF=9 applies if any of the parameters on which it is based is missing (QF=9) or is "NaN".

This section documents curation actions performed prior to publication review with the submitter, and additional information relevant to understanding and reusing this dataset. It distinguishes changes made to the submitted (meta)data from unresolved issues and/or enhancements that improve future reuse and interoperability.

CURATION ACTIONS PERFORMED ON DATA

- Imported original file "BCO-DMO_Lam_particle_v2.csv" into the BCO-DMO system.
- Renamed columns to comply with BCO-DMO naming conventions.
- Converted Start_Date_and_time_UTC from "%m/%d/%y %H:%M" format to datetime output format "%Y-%m-%dT%H:%MZ".
- Converted End_Date_and_time_UTC from "%m/%d/%y %H:%M" format to datetime output format "%Y-%m-%dT%H:%MZ".
- Converted Midcast_Date_UTC from "%m/%d/%y" format to date output format "%Y-%m-%d".
- Converted Midcast_Time_UTC from "%H:%M" format to time output format "%H:%M".
- Saved the final file as "1008015_v1_gp17-ant_major_particles_from_pumps.csv".

CURATION ACTIONS PERFORMED ON METADATA

- BCO-DMO's standard metadata entry and text formatting steps were performed. See: https://www.bco-dmo.org/how-to/standard-curation-edits

ISSUES POTENTIALLY IMPACTING REUSE

- The start, end, and mid dates/times are all the same. It's unclear which date/time is the actual start, end, and midpoint.
- It is unclear what "(GTC alt)" means in the Bottom_Depth column.

NSF Award Abstract:
The Amundsen Sea adjacent to Antarctica has gained increasing attention because of rapid melting of glaciers that drain into it. While most of the scientific and media attention has focused on how melting glaciers will affect sea level rise, there are also important consequences for ocean chemistry and biology. Parts of the Amundsen Sea have the highest rates of photosynthesis of all open water regions surrounding Antarctica, and this may be because melting glaciers are supplying essential nutrients such as iron. A detailed understanding of how melting glaciers affect the supply and removal of nutrients including iron is necessary to predict the biological, chemical, and climate consequences of melting glaciers.This project aims to study this system by focusing on the role that marine particles play in the supply and removal of trace nutrient levels. Marine particles include all suspended, solid material in seawater that derive from biological, chemical, and geological processes. Some types of marine particles supply nutrients to seawater, whereas other types remove nutrients from seawater. The investigators will determine the concentrations and chemical compositions of marine particles in the Amundsen Sea in order to understand which types supply and which types remove nutrients from seawater. This work will clarify the essential role of particles in the supply and removal of nutrients in this quickly changing part of the world. This work will train undergraduate and graduate students from three public US institutions in the west coast (University of California, Santa Cruz), northeast (University of Rhode Island), and southeast (University of Georgia). This project will also support a journalist to participate in the cruise and pitch, report, and write stories from the expedition to communicate the results of this collaborative project to the public.

The Amundsen Sea is a classic "warm Antarctic continental shelf", where intrusions of warm Circumpolar Deep Water (CDW) onto the shelf have resulted in the highest glacial basal melt rates on the Antarctic Margin. The US GEOTRACES program has been funded for a 60-day research cruise in the Amundsen Sea to bring geochemical tools to study the biogeochemical consequences of this high melt. Particles are a key parameter for all GEOTRACES section cruises because of their importance in the supply, internal cycling, and removal of many trace elements and isotopes (TEIs). Previous cruises to the Amundsen Sea have suggested that particulate Fe, abundant in meltwater-influenced regions, may be helping to fuel the high NPP in the Amundsen. Particles also play an essential role in the removal of dissolved Fe and other particle-reactive TEIs via scavenging. Indeed, models have shown that scavenging by particles is by far the largest loss term for dissolved Fe (dFe), even larger than biological uptake when integrated over the entire water column. So far, particles have been represented only as particulate organic matter (POM). The inclusion of other particle types besides POM is likely important for scavenging: for example, Fe and Mn (oxyhydr)oxides have been shown to be 1-3 orders of magnitude more efficient at scavenging some TEIs compared to other particle types, including POM. Thus, the composition of particles, not just their concentration, is important for the scavenging removal of TEIs. To address this gap in the understanding of particle biogeochemistry in the Amundsen Sea, this project has the following three main goals:

1) To determine the distributions of major and minor phases (particulate organic carbon, opal, CaCO3, lithogenic particles, Fe oxyhydroxides, Mn oxides), and trace element and suspended particulate mass concentrations of size fractionated particles collected by in-situ filtration.

2) To determine the speciation and bioavailability of particulate Fe in the Amundsen Sea to assess its role as a source and sink of TEIs.

3) To examine the factors affecting the formation, reactivity, and stability of Mn oxides in the Amundsen Sea.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

U.S. GEOTRACES extended its meridional transect, initiated on the 2018 GP15 Alaska-Tahiti expedition, south to the Antarctic ice edge and then east to Chile with GP17-OCE (December 2022 - January 2023). Because of the potentially important trace elements and isotopes (TEIs) inputs and transformations occurring in Antarctic waters and shelves, GP17 also had a second leg, GP17-ANT (November 29, 2023 - January 30, 2024) into coastal and shelf waters of Antarctica’s Amundsen Sea. Further information is available on the US GEOTRACES website.

NSF Project Title: Collaborative Research: Management and Implementation of US GEOTRACES GP17 Section: Amundsen Sea Sector of the Antarctic Continental Margin (GP17-ANT)

NSF Award Abstract:
This project will support the management and implementation of a 60-day research cruise to the Amundsen Sea sector of the Antarctic continental margin to collect samples for measurements of a broad suite of trace elements and isotopes ('TEIs'), as part of the U.S. GEOTRACES program. GEOTRACES is a global effort in the field of Chemical Oceanography, the goal of which is to understand the distributions of trace elements and their isotopes in the ocean. Determining the distributions of these elements and isotopes will increase the understanding of processes that shape their distributions and also the processes that depend on these elements. Key TEIs include essential micronutrients such as iron and zinc; 'tracers' such as aluminum, manganese, and isotopes of nitrogen, thorium and neodymium that can be used to investigate modern and ancient ocean processes; and elements such as lead that are indicative of human activities. In the Southern Ocean, the Antarctic continental margins are important as sources of micronutrient trace elements such as iron, which is required to support biological production and carbon export over the Antarctic shelf and in offshore waters of the Antarctic Circumpolar Current. Moreover, these regions are experiencing rapid environmental changes that are expected to impact oceanic circulation and biogeochemical cycles, for which TEIs provide crucial data needed to test and refine numerical models of the Earth system. The Amundsen Sea sector holds particular interest because of the pronounced, decadal-scale increases in the melting rates of glacial ice shelves that border the region, driven by intrusions of warm Circumpolar Deep Water onto the continental shelf. This melting has potentially major impacts on global sea level, on the formation of Antarctic Bottom Water in the Ross Sea, and on the regional ecosystem.

The cruise will comprise essential sampling operations (collection and shipboard processing) and ancillary measurements (hydrography, nutrients, algal pigments) in support of multiple, individual science projects, following the successful model of previous U.S. GEOTRACES cruises in the Atlantic, Pacific and Arctic ocean basins. The cruise will sample the ocean region between 100°W and 135°W, with stations ranging from 67°S in the Antarctic Circumpolar Current southward to the Amundsen Sea continental shelf, including stations adjacent to several rapidly melting ice shelves and in highly-productive shelf polynyas. Water column samples will be collected using conventional and trace-metal clean CTD-rosette systems, in-situ high-volume pumps, and a towed fish sampler or small boat, using established methods. Sampling time will also be provided for collection of sea ice, floating glacial ice, and seafloor sediments. To facilitate coordination with a complementary open-ocean cruise and ensure access to the study region to document the impact of biological processes, the cruise is planned for late austral summer (late January-late March). Beyond the disciplinary contributions, the proposed research will contribute knowledge concerning the cryosphere and its impacts on global sea level and ocean circulation, regional ecosystems and biological processes, ocean-atmosphere interactions, and past and future environmental change. The project will contribute to STEM education and outreach through the participation of an NSF-funded PolarTREC education professional, and a K-12 STEM program for students from underserved and underrepresented schools run by Rutgers University education specialists. To foster public engagement, the investigators will partner with the UCSC Science Communication Program to engage freelance science journalists to profile research in this spectacular and harsh Antarctic environment.

GEOTRACES is a SCOR sponsored program; and funding for program infrastructure development is provided by the U.S. National Science Foundation.

GEOTRACES gained momentum following a special symposium, S02: Biogeochemical cycling of trace elements and isotopes in the ocean and applications to constrain contemporary marine processes (GEOSECS II), at a 2003 Goldschmidt meeting convened in Japan. The GEOSECS II acronym referred to the Geochemical Ocean Section Studies To determine full water column distributions of selected trace elements and isotopes, including their concentration, chemical speciation, and physical form, along a sufficient number of sections in each ocean basin to establish the principal relationships between these distributions and with more traditional hydrographic parameters;

* To evaluate the sources, sinks, and internal cycling of these species and thereby characterize more completely the physical, chemical and biological processes regulating their distributions, and the sensitivity of these processes to global change; and

* To understand the processes that control the concentrations of geochemical species used for proxies of the past environment, both in the water column and in the substrates that reflect the water column.

GEOTRACES will be global in scope, consisting of ocean sections complemented by regional process studies. Sections and process studies will combine fieldwork, laboratory experiments and modelling. Beyond realizing the scientific objectives identified above, a natural outcome of this work will be to build a community of marine scientists who understand the processes regulating trace element cycles sufficiently well to exploit this knowledge reliably in future interdisciplinary studies.

Expand "Projects" below for information about and data resulting from individual US GEOTRACES research projects.