Spatiotemporal variability of sedimentary organic matter supply and recycling processes in coral reefs of Tayrona National Natural Park, Colombian Caribbean

Abstract

Abstract. Sediments are fundamental for the functioning of oligotrophic coral reef ecosystems, because they are major places for organic matter recycling. In Tayrona National Natural Park (TNNP), Colombian Caribbean, located between the population center Santa Marta (>455 000 inhabitants) in the southwest and several river mouths in the east, coral reef sediments experience pronounced changes in environmental conditions due to seasonal coastal upwelling, but knowledge on relevant spatiotemporal effects on organic matter supply to sediments and recycling processes is not available. Therefore, sediment traps were monthly deployed over 14 months complemented by assessment of sedimentary properties 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 contents and SOD increased significantly with decreasing distance to the eastern rivers, but only during upwelling. This suggests sedimentary organic matter supply control by nutrient-enriched upwelling waters and riverine runoff rather than by the countercurrent-located city of Santa Marta. Organic matter pulses caused C turnover rates of 4.4% h−1 that were more than 2-fold higher at water current-exposed compared to -sheltered sites. This indicates intense advective pore water exchange and ensuing rapid recycling of the supplied labile organic matter, particularly in the highly permeable water current-exposed silicate reef sands.