2023 GO-SHIP I05

Our planet and oceans are both variable and rapidly changing, and the Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP) seeks to document how the Earth is changing from one decade to the next.  The program makes high quality measurements of seawater chemistry, heat, and freshwater content from the ocean surface to the seafloor along specified lines that cross entire ocean basins, and seeks to repeat these measurements each decade.  GO-SHIP is an international effort with contributions from many nations.  The I05 (not the freeway… see the map) line crosses the Indian Ocean.  It is one of the longer lines that is traditionally measured in one continuous research cruise and it has been 14 years since this line was last measured.  This is one of the longest gaps for the lines traditionally measured by US teams, and this area represents a critical knowledge gap for our understanding of global and regional ocean heat, carbon, and freshwater change.  The line crosses the Leeuwin Current adjacent to Australia–the only poleward flowing subtropical eastern boundary current–passes over the complex topography of the South Indian Ocean, and finishes by crossing the highly energetic Agulhas Current near South Africa.

Key and anticipated uses for these and all GO-SHIP data include:

• • Model calibration and validation
  • Carbon system studies including the inference of the anthropogenic carbon content of seawater (or how much additional carbon is in seawater due to human CO2 emissions)
  • Heat and freshwater storage and flux changes    Deep and shallow water mass and ventilation studies    Calibration of autonomous sensors

This occupation will be the first time that metagenomic information and particulate organic carbon measurements will be made on the I05 line.  This effort is through the Bio-GO-SHIP program, and these measurements will provide the foundation for future studies examining how ocean biology is shifting in response to global changes.

The specific goals of this cruise are as follows:

• • Re-occupation of the historic stations in this line spanning from Australia to South Africa at the nominal 30 nautical mile resolution.
  • As timing allows, repeat stations dedicated to obtaining higher resolution measurements while crossing important bathymetric features such as deep ocean ridges.
  • A second cast dedicated to biological measurements will be collected at select stations throughout the line.
  • Deployment of:
    • 7 EM Apex (“SQUID” floats, Sampling QUantitative Internal-wave Distribution) that measure, temperature, salinity, velocity, ocean turbulence, and diffusivity
    • 8 floats (through the SOCCOM and GO-BGC programs) that measure biogeochemical properties in addition to measuring the temperature and salinity of seawater
    • 12 Directional Wave Spectra Barometric Drifters from the Indian National Centre for Ocean Information Services (INCOIS) and
    • 10 drifters from NOAA’s AOML laboratory.

GO-SHIP I05 will depart Fremantle, Australia on the R/V Roger Revelle on July 22, 2023 and arrive in Cape Town, South Africa on September 14, 2023.

Please join along on the journey by following the expedition blog!

Chief Scientist: Brendan Carter (UW)
Co-chief Scientist: Kay McMonigal (UAF)

Figure 1: Plot of cruise track. GO-SHIP I05 will depart Fremantle, Australia on the R/V Roger Revelle on July 22, 2023 and arrive in Cape Town, South Africa on September 14, 2023. The upper image shows just the cruise track for the I05 expedition. The lower image shows the cruise track relative to previous float deployements in the region.