Physical Oceanography

Ocean currents and waves are like the life blood of coral reef ecosystems: they bring nutrients, prey, and new recruits, and may carry away or dilute particulates and harmful chemical compounds. Currents are the medium connecting reefs with estuaries, channels, mangrove forests and seagrass beds inshore, and with the deeper oceans that invariably lie offshore of the reef. Together with direct air-sea exchanges of heat, water, gases, momentum, and nutrients at the sea surface, ocean currents largely control the physical and chemical environment of coral reefs. Yet while significant advances have occurred, especially over the past 30 years, our scientific knowledge of the physical oceanography of coral reefs is far from complete.

The complex physical interplay between wind, waves, water density (which is determined largely by sea temperature, but also by salinity), pressure, solar radiation, and the hard boundaries of the ocean make physical oceanography a challenging subject. For coastal oceanography, especially near reefs, the complexity of and rapid gradients in sea-floor bottom topography heighten these challenges. Furthermore, wind and waves in such environments may cause relatively violent water motions and heavy sediment loads, and the ongoing ecology of the reef itself may cause significant biofouling. Thus, the gathering of useful physical data to enhance our understanding of coral reefs becomes a very significant operational and practical challenge in its own right.

Ocean currents are among the most difficult variables to directly measure in situ (i.e., in the natural environment of the reef). Because of the paucity of direct measurements of currents on reefs, CHAMP researchers are using other, more easily measured variables like sea and air temperature, wind, light attenuation, and coastal ocean color (from satellites) as proxies for detecting and interpreting significant reef circulation events. The onshore flux page describes these efforts in more detail. Understanding the connection of coral reefs with the wider world through larger-scale oceanography is also an active area of research using shipboard measurements.

Finally, sea temperature, a physical oceanographic variable, is in itself a significant driver of coral reef ecosystems. Understanding the balance of air-sea fluxes, convection, and ocean currents that force sea temperature change over reefs, the so-called reef heat budget, is a major area of research within CHAMP right now.

Modeling Onshore FluxThe CHAMP project has developed an ecoforecast model that seeks to now-cast onshore flux directly, by matching characteristic patterns in physical data on the reef.

Reef Heat BudgetsQuality-controlled, in situ data have been combined with high-resolution atmospheric reanalyses from the NOAA National Centers for Environmental Prediction (NCEP), together with models and satellite data, to estimate surface radiative and turbulent heat fluxes and heat advection for monitored sites.