Unlocking past and present climatic and anthropogenic drivers of environmental change influencing Miri–Sibuti Coral Reefs National Park (Borneo, Malaysia)

Corals are calcifying organisms that predominantly live in warm shallow waters across the tropics. Coral reefs are known to harbour as much as 25 % of all marine species thereby making them the richest marine ecosystems on the planet. Coral species incorporate a diverse array of trace elements naturally present in the surrounding seawater into their skeleton upon calcification in similar concentrations or depending on local seawater temperature. As such, analysing the coral skeleton’s geochemistry and isotopic signature across cores sampled from different colonies allows us to build various records of past environmental conditions. We used δ18O, Sr/Ca, B/Ca, and Ba/Ca records as proxies for hydroclimate, temperature, and sediment in river discharge to investigate the human and climatic drivers of environmental change in the Miri–Sibuti Coral Reef National Park in Sarawak, Malaysian Borneo. Here, we first use the corals δ18O signature as a proxy for local hydroclimate and show the importance of record replication, the use of an appropriate instrumental record and more importantly, a growing influence of the El Niño Southern Oscillation phenomenon on the hydroclimate of this region. We then test the capacity of the Ba/Ca proxy to record river discharge based on available instrumental data and show that corals are able to record an increased river discharge linked to growing deforestation since the mid 90s. Based on this chapter’s results, we then produce extended records to uncover the onset of industrial deforestation in the middle of the 20th century in this region and link it to local and regional deforestation and land use records. This thesis emphasises the significance of utilising geochemical proxies to compensate for the absence of instrumental data in remote regions. These proxies prove invaluable in supplying essential information to inform evidence–based policies aimed at safeguarding local ecosystems.