Abstract
Abstract. Sediments are fundamental for the function of oligotrophic coral reef ecosystems because they are major places for organic matter recycling. The Tayrona National Natural Park (TNNP, Colombian Caribbean) is located between the population center Santa Marta (>455 000 inhabitants) in the southwest and several river mouths in the east. Here, coral reef sediments experience pronounced changes in environmental conditions due to seasonal coastal upwelling, but knowledge of relevant spatiotemporal effects on organic matter supply to the sediments and recycling processes is not available. Therefore, sediment traps were deployed monthly over 14 months complemented by assessment of sedimentary properties (e.g., porosity, grain size, content of particulate organic matter and pigments) and sedimentary O2 demand (SOD) at water-current-exposed and sheltered sites along distance gradients (12–20 km) to Santa Marta and the eastern river mouths (17–27 km). Findings revealed that seasonal upwelling delivered strong (75–79% of annual supply) pulses of labile organic matter mainly composed of fresh phytoplankton detritus (C : N ratio 6–8) to the seafloor. Sedimentary chlorophyll a contents and SOD increased significantly with decreasing distance to the eastern rivers, but only during upwelling. This suggests sedimentary organic matter supply controlled by nutrient-enriched upwelling waters and riverine runoff rather than by the countercurrent-located city of Santa Marta. Organic matter pulses led to significantly higher SOD (more than 30%) at the water-current-sheltered sites as compared to the exposed sites, ensuing a rapid recycling of the supplied labile organic matter in the permeable silicate reef sands.
Highlights
Marine shelf sediments are the major sites for mineralization and nutrient regeneration of organic matter derived from pelagic primary production and terrestrial input
The organic matter supplied to Tayrona National Natural Park (TNNP) reef sediments was generally higher at the wind, wave- and water-currentexposed site and increased significantly during seasonal upwelling
A higher accumulation of organic matter and increased sedimentary O2 demand (SOD) were observed at the water-current-sheltered sites where the sedimenting material was allowed to settle due to lower hydrodynamics
Summary
Marine shelf sediments are the major sites for mineralization and nutrient regeneration of organic matter derived from pelagic primary production and terrestrial input (reviewed by Arndt et al, 2013). The efficiency of sedimentary organic matter remineralization largely depends on the properties of sediment e.g., grain size (Zobell, 1938; Newell, 1965; Meyer-Reil, 1986), permeability (Webb and Theodor, 1968; Precht and Huettel, 2004; Rusch et al, 2006), carbonate content (Capone et al, 1992; Rasheed et al, 2003), sorption capacity
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