The influence of a sandy substrate, seagrass, or highly turbid water on albedo and surface heat flux
Fogarty, M.C.; Fewings, M.R.; Paget, A.C.; Dierssen, H.M. (2018). The influence of a sandy substrate, seagrass, or highly turbid water on albedo and surface heat flux. JGR: Oceans 123(1): 53-73. https://dx.doi.org/10.1002/2017jc013378 In: Journal of Geophysical Research-Oceans. AMER GEOPHYSICAL UNION: Washington. ISSN 2169-9275; e-ISSN 2169-9291, more |  |
| Authors | | Top | - Fogarty, M.C.
- Fewings, M.R.
- Paget, A.C.
- Dierssen, H.M., more
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| Abstract | Sea‐surface albedo is a combination of surface‐reflected and water‐leaving irradiance, but water‐leaving irradiance typically contributes less than 15% of the total albedo in open‐ocean conditions. In coastal systems, however, the bottom substrate or suspended particulate matter can increase the amount of backscattered light, thereby increasing albedo and decreasing net shortwave surface heat flux. Here a sensitivity analysis using observations and models predicts the effect of light scattering on albedo and the net shortwave heat flux for three test cases: a bright sand bottom, a seagrass canopy, and turbid water. After scaling to the full solar shortwave spectrum, daytime average albedo for the test cases is up to 0.20 and exceeds the value of 0.05 predicted using a commonly applied parameterization. Daytime net shortwave heat flux into the water is significantly reduced, particularly for waters with bright sediments, dense horizontal seagrass canopies < 0.25 m from the sea surface, or highly turbid waters with suspended particulate matter concentration ≥ 50 g m−3. Observations of a more vertical seagrass canopy within 0.2 and 1 m of the surface indicate the increase in albedo compared to the common parameterization is negligible. Therefore, we suggest that the commonly applied albedo lookup table can be used in coastal heat flux estimates in water as shallow as 1 m unless the bottom substrate is highly reflective or the water is highly turbid. Our model results provide guidance to researchers who need to determine albedo in highly reflective or highly turbid conditions but have no direct observations. |
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