SAGE Overview

Objectives

This experiment combines seven main research objectives considering:

  • Quantification of gas transfer fluxes and velocities
  • Physical processes affecting gas transfer
  • Ecosystem interactions controlling dissolved DMS concentration and CO2 removal
  • Impact of iron availability upon phytoplankton productivity and its influence upon dissolved gas concentration
  • Impact of photochemistry in the surface ocean on dissolved gas concentration and air–sea exchange
  • Fate of DMS in the atmosphere and aerosol condensation nuclei production from chemical transformation in the atmospheric boundary layer
  • Role of aggregation in the timing and magnitude of export processes

The proposed site for SAGE is south east of New Zealand.

The experiment will be conducted from NIWA’s ocean-going research vessel, RV Tangaroa.

Site Selection

The site of the experiment is chosen to satisfy a number of criteria:

  • Relatively stable water mass allowing the tracer labelled patch to be tracked for up to 20 days (one of the most difficult criteria to satisfy)
  • Mixing Layer Depth of 30 to 60 m for preservation of SF6 and dilution of iron
  • High Nutrient, low chlorophyll (HNLC) waters receptive to an iron-induced bloom without limiting macronutrient
  • Range of windspeeds for the study of the gas exchange coefficient–windspeed relationship

Tasks & Teams

1. Labelled patch tracking, advection and diffusion of patch

This group is responsible for labelling and mapping the 10 km length-scale fertilised SF6 patch. Vertical profiling and mapping of SF6 will provide estimates of vertical and horizontal diffusivity. Alongside the mapping, continuous underway measurements will be made of T, S, nutrients fluorescence, FRRF, ADCP currents. Vertical information on SF6 will be provided from CTD casts including collection of samples for subsequent 3-Helium analysis.

Cliff Law, NIWA (SF6, diffusivity)
Ed Abraham, NIWA (SF6, diffusivity)
Mark Hadfield, NIWA (site selection)
Peter Hill, NIWA (GCs, electronics)
David Ho, LDEO, Columbia University, (3He)
Andrew Marriner, NIWA(SF6)
Matt Walkington, NIWA (CTD)

2. Iron chemistry

This team will be responsible for mapping patch dissolved iron, iron speciation, ligands and particulate iron. A key role is keeping track of iron availability in the early stages of the experiment following fertilisation in order to provide information for planning possible re-infusions. Iron mapping will be conducted at night at the same time as SF6 mapping, with the fish deployed whilst steaming. Iron mapping is likely to be done every second night to monitor patch evolution. For determining whether iron reinfusion is required, a sample will be collected every day from the centre of the patch, during or just after SF6 mapping has been completed.

In addition to oceanographic measurements, aerosol samples will be collected on the transit legs for quantifying atmospheric iron input. A high-volume sampler will be used with an inlet on the tower mounted in the bow.

Michael Ellwood, NIWA (Fe, ligands)
Doug Mackie, University of Otago (Fe)

3. Ocean atmosphere gases

This team will combine point sampling atmospheric and oceanographic and atmospheric measurements of CO2, and DMS to estimate air-sea exchange fluxes. For DMS, in addition to underway dissolved-gas measurements, we will measure the flux into the atmosphere using the relaxed eddy accumulation technique with a sonic anemometer mounted on top of the foredeck mast. This technique partitions gas samples into the concentrations associated with updraft and downdraft eddies in air arriving at the mast and, in combination with the seawater concentration, allows the gas exchange coefficient to be calculated. For CO2, a combination of pCO2 and atmospheric measurements will be made to allow exchange coefficient estimates of CO2 fluxes. Additional measurements include, pH, alkalinity, atmospheric and dissolved oxygen. Measurements of Ne, Ar and dissolved gas partial pressure will be used to provide an estimate of bubble effects.

Murray Smith, NIWA (REA, micromet)
Kim Currie, NIWA (CO2)
Mike Harvey, NIWA (DMS, REA)
David Ho, LDEO, Columbia University (3He, Ne, Ar, δ17O)
Graham Jones, Southern Cross University (DMS)
David Katz, University of Rhode Island (Gas tension device: pN2/pO2, Winkler)
Cliff Law, NIWA (SF6)
Burns Macaskill, NIWA (pH, alkalinity)
Rona Thompson, NIWA/Victoria University (O2/CO2 ratio)

4. Surface Physics

This group will measure the state of the sea–surface interface to examine the role of waves, skin temperature and near surface ocean stability in governing gas exchange. Measurements include radiometric and radar measurements from sea-surface viewing instrumentation on the vessel and over side and from Zodiac deployments of microturbulence profilers. On suitable days, the physics deployments will be combined with floating flux chamber measurements for gases.

Craig Stevens, NIWA (SCAMP, TRAMP)
Ed Abraham NIWA (ADCP, FRRF)
John McGregor, NIWA (radar)
Peter Minnett, RSMAS, University of Miami (M-AERI radiometer)
Murray Smith, NIWA (Vector, radar)
Brian Ward, WHOI (SkinDeep)

5. Biological processes and DMS

This group will investigate the role of the ecosystem in governing the production of dissolved DMS. In addition to a comprehensive suite of biological measurements, on-board experiments are planned to look at the biological production and utilisation of DMSP and DMS.

Water column measurements include measurement of: chlorophyll a, size-fractionated chlorophyll (0.2–2, <20, Total), HPLC samples, bacteria –microzooplankton –( flagellates & ciliates), mesozooplankton – phytoplankton biomass. Daily primary production will be estimated from simulated in-situ measurements. Accompanying column measurement of nutrients and DMS(P) will be made.

Production DMSPp will be measured using a dilution grazing experiments. The role of microzooplankton and mesozooplankton grazing will be investigated. Bacterial production will be measured using tritiated thymidine. Experiments will be conducted to estimate bacterial turnover of DMSP/DMS.

Julie Hall, NIWA (microbial, flow cytometry, bacteria)
Stephen Archer, Plymouth Marine Laboratory (DMS p, ecosystem interactions)
Michael Bender, Princeton University (δ17O, productivity)
Graham Jones, Southern Cross University (DMS, DMSp,DMSO, HPLC pigments)
Jorma Kuparinen, NIWA (flow cytometry, microzoo, bacteria)
Jill Peloquin, VIMS (primary productivity, Chla)
Stu Pickmere, NIWA (Nutrients)
Karl Safi, NIWA (grazing, taxonomy)

6. Aquatic Photochemistry / greenhouse gases

This module will look at the photochemical production of carbon monoxide in surface waters with a combination of in-situ chamber and incubation techniques. Measurements of light absorption by dissolved organic matter and UV_R profiles in the water column will be obtained, along with water column sampling for CDOM and CO.

Nitrous oxide production will be studied from concentration profile measurements from CTD samples within the mixed layer and below the pycnocline.

Cliff Law, NIWA (CO, NO, chamber)
Andrew Marriner, NIWA (GC)
Lori Ziolkowski, Dalhousie University (CO, CDOM)

7. Atmospheric Chemistry

This group will examine the atmospheric gas and aerosol products resulting from DMS oxidation. SO2 will be measured using an HPLC fluorescence technique, size-resolved aerosol chemistry will be measured by collecting samples on Tedlar film using a Berner impactor with four stages of size segregation: 4–10 um, 1.1–4 um, 0.55–1.1 and less than 0.55 µm with analysis by IC. Particle sizing will be done on occasion using a ASASP-100X laser optical sampler, which bins particles into 15 channels between 0.1 and 3 µm diameter, used to give an estimate of the concentration of mechanically generated sea salt aerosol. Condensation nuclei (>10 nm) and ultrafine nuclei (>3 nm) will be measured using TSI 3010 and 3025A nuclei counters, used to give an indication of any events of new aerosol particle formation.

Mike Harvey, NIWA (DMS, ASASP)
Jill Cainey, Cape Grim, Australia (SO2, UCN)
Dawn Devries, University of Colorado (aerosol, SO2)

8. Export Processes and Biophysical Moorings

Floating sediment trap deployments will be carried out both in the patch (5 deployments) and out of the patch (3 deployments). Measurement from the traps will be used to determine the timescales of aggregation and export processes and linkages to temporal changes in physical, chemical and biological processes within a bloom. The size, composition and flux magnitude of exported organic matter will be calculated with chemical fluxes of (POC, PP, PN, PSi) in and out of the SF6-defined patch including profiles from CTD casts.

At the end of the voyage, the two NIWA biophysical moorings will be serviced: the northern mooring at 41°11.28’S 178°28.62’E and southern mooring at approximately 46°38.202’S 178°33.486’E.

Scott Nodder, NIWA (sediment traps)
Bill Main, NIWA (iron, moorings)

Science Plan

The Science Plan is available as a PDF file.