Penetration of ultraviolet radiation in the waters of the estuary and Gulfof St. Lawrence

Citation
P. Kuhn et al., Penetration of ultraviolet radiation in the waters of the estuary and Gulfof St. Lawrence, LIMN OCEAN, 44(3), 1999, pp. 710-716
Citations number
41
Categorie Soggetti
Aquatic Sciences
Journal title
LIMNOLOGY AND OCEANOGRAPHY
ISSN journal
00243590 → ACNP
Volume
44
Issue
3
Year of publication
1999
Pages
710 - 716
Database
ISI
SICI code
0024-3590(199905)44:3<710:POURIT>2.0.ZU;2-X
Abstract
Downwelling ultraviolet (UV) irradiance (290-400) nm was measured at 1-nm i ntervals in the surface waters of the estuary and Gulf of St. Lawrence, Can ada, in September 1996 and June and September 1997. Measurements were made with an Optronic Laboratories OL 754-O-PMT spectrophotometer equipped with a fiber-optic cable and an underwater sensor. Fluxes greater than the instr ument's noise equivalent irradiance (NET) level of 1 x 10(-5) Wm(-2) nm(-1) just below the sea surface were measured at wavelengths of greater than or equal to 294 Mn. At 310 nn, the diffuse attenuation coefficient (K-d) rang ed between 0.7 and 4.5 m(-1), with corresponding 10% depth penetrations bet ween 4 and 0.5 m. This represents close to half of the summer mixed-layer w ater column in the Gulf of St. Lawrence. The following correlation coeffici ents were found: 0.81 between dissolved organic carbon (DOC) and K-d, 0.73 between chlorophyll a (Chl a) and K-d, and 0.73 between Chi a and DOC. The spectral variation of K-d suggests that yellow substance, and therefore DOC , is responsible for UV attenuation in these bodies of water.