A photometer for the continuous measurement of calcite-dependent light scatter in seawater

Katherine A. Kilpatrick, William M. Balch, Yuntao Ge, Kenneth J. Voss

Research output: Contribution to journalConference articlepeer-review

3 Scopus citations


Biogenically-produced calcite represents a significant source of light scatter in the ocean, poorly defined in space and time. One reason for this lack of observations is that standard shipboard techniques for measuring light scatter are slow and labor intensive. We describe an automated photometer for measuring 90° light scatter due to calcite on time scales as short as a minute. Raw seawater continuously flows through a 1 mL glass cuvette illuminated by a helium-neon laser. A photodiode is used to measure the 90° light scatter of particles in the incident beam. During each sampling interval, a calibrated addition of weak acid lowers the seawater pH to dissolve the calcite and another 90° light scatter measurement is made. Standard curves are prepared using calcium carbonate coccoliths from the coccolithophore Emiliania huxleyi. The relationships between acid-labile light scatter and coccolith abundance give an r2 of 0.96-0.99. The light scatter photometer is coupled to a fluorometer, temperature and salinity probe to relate the suspended calcite concentration to algal distributions and hydrography. We show some examples of its performance at sea.

Original languageEnglish (US)
Pages (from-to)512-521
Number of pages10
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - Oct 26 1994
EventOcean Optics XII 1994 - Bergen, Norway
Duration: Jun 13 1994Jun 15 1994

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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