Spectrophotometer analysis of Holocene sediments from an anoxic fjord: Saanich Inlet, British Columbia, Canada

A borehole core through the Holocene sediments of Saanich Inlet (British Columbia, Canada) was analyzed using high-resolution spectrophotometry to determine whether spectral–signal variations can be used as environmental/climatic proxies. The effects of post-drilling oxidation and water loss on the core sample were assessed by comparing spectral measurements taken onboard the research ship immediately after the core was opened with shore-based measurements taken one year later. For Saanich Inlet sediments, the shore-based measurements provided more reliable indications of the degree of basin anoxia. Our spectral analyses allowed us to identify all the major features of the Saanich Inlet sediment sequence (Mazama ash and Fraser River Drainage stratigraphic markers, oxygenation state of the basin). By using the first derivative value at 675 nm as a proxy for changes in organic matter content and the colorimetric parameter b⁎ as an indicator of diatom content, we were able to recognize changes in terrestrially derived organic matter (OM) and diatom concentrations in the sediment. We suggest that these variations are due to changes in upwelling intensity and fluctuations in sea level during the Holocene. Our results confirm the potential value of spectrophotometry in identifying sediment composition and in reconstructing paleoenvironments.