Guide to Bio and Biogeochemical Profiling Floats

While the initial program started in the late 1990s, it was not until 2000 that deployment of the floats started. Argo now consists of a fleet of almost 4000 currently operating drifting profiling floats deployed worldwide, with the total deployment to-date nearing 13,000. Because the typical lifetime of an Argo float is 4-5 years, maintaining this array requires replacement of about 800 floats per year. The array provides around 100,000 observations per year, and floats operate throughout all the ice-free deep-ocean areas of the world.

The Argo float network has played a key role in our understanding of ocean dynamics and warming. The network’s creation was a a major step forward in the ability to broadly monitor the ocean's temperature and salinity on a global scale, at higher frequency and lower cost than previously possible with ship-based monitoring. The program achieved its first goal of 3000 operating floats in October 2007, and on 30th October 2012 another milestone of one million data profiles was achieved (twice the amount collected by research vessels during the previous 100 years).

From temperature and conductivity, salinity and density can be calculated. Seawater density is important in determining large-scale motions in the ocean. Average current velocities at 1000 m are directly measured by the distance and direction a float drifts while parked at that depth, which is determined by GPS or Argos system positions at the surface. The data is transmitted to shore via satellite, and are freely available to everyone, without restrictions.

While the autonomous profiling floats for the Argo program were initially designed for physical observations, float technologies have evolved to include a broad range of biogeochemical measurements.

For the better part of 10 years, Argo-style floats were used primarily for collection of ocean temperature, salinity, and current data. This however is only collecting the physical properties of the ocean, not the ocean’s interior biology and chemistry, which can shed light on the base of the ocean’s food web and the amount of carbon that is absorbed by the oceans.

Before 2014, availability of ocean biological and biogeochemical data were limited, as biogeochemical monitoring programs similar to the Argo program did not exist. A need for an advanced biogeochemical float was apparent. While ocean color satellite imagery provided ocean basin-scale information on surface chlorophyll distributions, routine sampling of the vertical distributions of the biogeochemical properties on ocean basinscales had yet to be accomplished.

New technological advances in both sensor technologies and autonomous profiling platforms provided a pathway to accomplish this goal.

This broad product suite of biogeochemical sensors for long-term observing paved the way for incorporation into global observing networks. Building on these successful efforts, Sea-Bird Scientific developed the Navis Autonomous Profiling Float with Biogeochemical Sensors (commonly referred to as the Navis BGC).

The Navis BGCi family of floats has helped propel biological and biogeochemical ocean research since 2013.

The Navis BGCi float is now available with integrated pH and nitrate measurements for use in carbon cycling, nitrogen cycling, and community production studies. The Float Deep SeaFET™ ocean pH sensor uses the field-validated MBARI/SIO/Honeywell Deep-Sea DuraFET technology to measure pH on board the Navis BGCi float.

The Deep SUNA utilizes the proven MBARI-ISUS nitrate measurement technology and is in extensive use worldwide. The nitrate algorithm incorporates a temperature-dependent correction of the observed bromide absorption spectrum. Both the Float Deep SeaFET and Deep SUNA incorporate physical property data from the SBE 41N CTD to provide corrected data to the end user.

SOCCOM stands for Southern Ocean Carbon and Climate Observations and Modeling, whose stated mission is to drive a transformative shift in the scientific and public understanding of the role of the vast Southern Ocean in climate change and biogeochemistry.

The international Argo program has deployed thousands of autonomous floats to measure temperature and salinity in the world’s oceans. The SOCCOM project is augmenting conventional Argo floats with biogeochemical sensors to measure carbon (pH), nutrients (nitrate), and oxygen.

SOCCOM is the world’s first large-scale biogeochemical Argo deployment. The project will increase the number of biogeochemical measurements made monthly in the Southern Ocean by 10-30 times (more in the Southern Hemisphere winter, when observations are scarcest), and the data will be made freely available to the public. SOCCOM is also unique in combining an innovative observational program with a strong modeling program, and is integrating professional outreach partners into the program.

From soccom.princeton.edu