Paleoceanographic changes

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If Vtii/Ptii = 1 then the accumulation of °Thxs in marine sediments would provide an assessment of their sedimentation rate. For instance, if Pm is N dpm m yr , and N dpm are found in the upper 1 cm of 1 m of seafloor, then the sedimentation rate must be lcmyr Sedimentation rate is an important variable in paleoceanographic reconstruction as it provides the timescale for the continuous record of environmental change recorded in marine sediments. Sedimentation rate is also a key geochemical variable as sediments are the major sink for most chemical species in the ocean. A tool allowing assessment of past sedimentation rates is therefore an appealing prospect. 

Postdepositional changes can obscure the sedimentary paleoceanographic record. Fortunately, these alterations follow predictable geochemical principles, making it... 

The most common paleoceanographic proxy used to reconstmct past changes in the oceanic N cycle is the of total combustible, or bulk, sedimentary nitrogen (hereafter d Ntuik). Such measurements provide a record, with a variable degree of accuracy, of the N sinking out of the surface ocean at times past (Altabet and Francois,... 

A more significant source of variation in Aq is change in particle flux, which has unquestionably occurred. Indeed, it is the variations in flux that are of greatest interest in paleoclimatic and paleoceanographic studies the traditional °Th and Pa methods do not resolve them but instead average over them. This point is taken up further in the next section. 

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