The ocean's biological carbon pump plays a major role in the global carbon cycle. Particulate carbon pools in the ocean turnover on weekly time scales making it difficult to observe them from ships. Better observations of key biological pump variables, including the concentration variability of Particulate Inorganic Carbon and Particulate Organic Carbon (PIC and POC) will enable prediction of the evolving carbon cycle of the ocean.

UC Berkeley, WETLabs Inc., Scripps Instrument Development Group, and Lawrence Berkeley National Laboratory worked to transition an advanced low-power full ocean profiling prototype sensor for particulate inorganic carbon (PIC) to robust ‘commercial quality’ forms. The group also perfected methodology for optical sensing of POC using commercial transmissometers. Sensors were demonstrated by deployment on ship-lowered instrument packages and on autonomous ocean profiling floats.

The new PIC sensor operates by detecting birefringent calcium carbonate particles in a transmissometer beam. It does this using laser light, a polarizer aligned with the laser, a 25 cm water path and a polarizer aligned to block the laser light (Figure 1). When calcium carbonate particles are present in the water path of the instrument, the laser light is depolarized and photons pass to the detector.

Project members engaged in a series of short oceanographic expeditions from 2010-2013 to incrementally test candidate instrument designs. In 2012, a first design utilizing open cells was successful; In 2013, the project achieved a major mile stone... three new PIC sensors yielded identical profiles during profiling to 2000 meters (Figure 2). This led to the deployment of two of the PIC sensors on Berkeley's robotic ocean profiling Carbon Explorer floats in 2013 (Figure 3). For the first time, data on calcium carbonate particle concentrations in the ocean watercolumn were relayed via satellite in real time from the remote ocean by the Carbon Explorers as they yo-yoed from 1000 m depths to the surface and back on a daily basis. The project discovered long term issues during the 100 day long CE deployments. Sensors were refined and tested at sea to depths of 4000 m in August 2016.

The calibration of the sensors has been carried out to sea utilizing particle samples from filtering 1 liter seawater samples and from 1000 liter volumes of seawater processed by large volume in-situ filtration pumps. The process of calibration is ongoing; however we have been able to demonstrate that the primary signal seen by the sensor is proportional to calcium carbonate particle concentrration in the water.

There have been two journal articles and 9 meeting presentations of project results.

The project has laid the basis for the commercialization of the PIC sensor and its availability to the international oceanographic community. Transmissometer products marketed by WETLabs, Inc. improved in their stability as a direct result of this project. Protocols for improved optical sensor accuracy have been communicated to and used by the oceanographic community.

This project provided hands-on research experience in the laboratory and at sea for UC Berkeley undergraduates. Since project inception 28 UC Berkeley undergraduates have participated in 8 expeditions (13F; 15M - including 4 Hispanic Americans (1F/3M); 4 Asian Americans (2F/2M); and 2 with disabilities (1F/1M); 12 (6F/6M) have been accepted to graduate schools in oceanography, chemistry, environmental law and engineering.

In Feb. 2013, we began a collaboration with the San Francisco Exploratorium to improve public outreach in the area of the science of the ocean’s carbon cycle. As an example of this outreach, one of our undergraduates, Jessica Kendall-Bar, lead a public presentation in the Exploratium series: "Everything Matters: Tales of the Periodic Table: Calcium", March 16 2017.

Last Modified: 05/30/2017
Modified by: James K Bishop