Carbonate sediments in a cool‐water macroalgal environment, Kaikoura, New Zealand

Abstract

Brown and red, and to a lesser extent green, macroalgae are a hallmark of intertidal rocky coasts and adjacent shallow marine environments swept by stormy seas in middle and high latitudes. Such environments produce carbonate sediment but the sediment factory is neither well‐documented nor well‐understood. This study documents the general marine biology and sedimentology of rocky coastal substrates around Kaikoura Peninsula, a setting that typifies many similar cold‐temperate environments with turbid waters and somewhat elevated trophic resources along the eastern coast of South Island, New Zealand. The macroalgal community extends down to 20 m and generally comprises a phaeophyte canopy beneath which is a prolific rhodophyte community and numerous sessile calcareous invertebrates on rocky substrates. The modern biota is strongly depth zoned and controlled by bottom morphology, variable light penetration, hydrodynamic energy and substrate. Most calcareous organisms live on the lithic substrates beneath macroalgae or on algal holdfasts with only a few growing on macroalgal fronds. A live biota of coralline red algae [geniculate, encrusting and nodular (rhodoliths)], bryozoans, barnacles and molluscs (gastropods and epifaunal bivalves), together with spirorbid and serpulid worms, small benthonic foraminifera and echinoids produce sediments that are mixed with terrigenous clastic particles in this overall siliciclastic depositional system. The resultant sediments within macroalgal rocky substrates at Kaikoura contain bioclasts typified by molluscs, corallines and rhodoliths, barnacles and other calcareous invertebrates. In the geological record, however, the occurrence of macroalgal produced sediments is restricted to unconformity‐related early transgressive systems tract stratigraphic intervals and temporally constrained to a Cenozoic age owing to the timing of the evolution of large brown macroalgae.

Physical oceanography of New Zealand/Aotearoa shelf seas – a review

“…The canyon starts within a km of shore before running 60 km offshore to a depth of over 1 km (Lewis and Barnes 1999). This provides a pathway for productivity-enhancing nutrients in the Kaikoura region (Reid et al 2011). There is at least one documented case of northerly winds inducing upwelling off Kaikoura (Heath 1972), and such upwelling is often associated with high productivity in the region (e.g.…”

Production of dissolved carbon and alkalinity during macroalgal wrack degradation on beaches: a mesocosm experiment with implications for blue carbon

“…This is likely because the organic acids leaching out of the kelp first lower the pH and shift the carbonate equilibrium. However, the release of organic acids in contact with seawater and the TA production from sulphate reduction reduces the available O 2 but favours calcium carbonate dissolution, which in turn raises the pH (James and Bone 2011;Reid et al 2011). The oxidant concentration for sulphate reduction has been reported as 28 mM, using the approximate concentrations in seawater (Santos et al 2021).…”

Warm‐temperate, marine, carbonate sedimentation in an Early Miocene, tide‐influenced, incised valley; Provence, south‐east France

“…Recent studies indicate that lithic substrates are not only areas of algal attachment, but that extensive growth of macroalgae also creates a somewhat sheltered environment that is colonized by articulated coralline algae, barnacles, bryozoans (particularly articulated and fenestrate forms), gastropods and echinoids (James & Bone, ; Reid et al ., ). The algal fronds themselves are not generally encrusted, except for some phaeophytes such as Ecklonia sp., whose blades can be partially covered with spirorbid worms and bryozoans.…”