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Mangrove forests serve as significant carbon sinks and play a crucial role in mitigating climate change. Currently, the response of mangroves to intensified climate change and human activities, and the factors that influence the magnitude of carbon storage in their sediments remain uncertain. To address these questions, two sediment cores were collected from the mangrove reserve in Pearl Bay, Guangxi, China. The activity of 210Pb in the sediment, grain size, bulk elemental composition, stable carbon isotopes, lignin, and different sediment organic matter (OM) fractions were investigated to determine the local mangrove's response to climate change and human activities, as well as the factors influencing its carbon storage. The results showed mangrove forests with lower tidal ranges, slower sedimentation rates, and where OM predominantly originated locally tend to have larger carbon stocks. The mangrove OM (MOM) decreased progressively from the bottom to the top of the cores, indicating that the mangroves in Pearl Bay have possibly undergone degradation, which was further substantiated by the decrease in lignin content. Based on these results, the entire cores were divided into two stages: stable stage 1 (1963-2001) and degradation stage 2 (2001-2020). The cause of the mangrove degradation is likely due to the impact of human activities; however, these impacts are anticipated to gradually lessen in the future due to mangrove protection policies. Our results indicate that lignin can track and predict mangrove growth trends and provide guidance for the sustainable management of mangrove ecosystems. [ABSTRACT FROM AUTHOR]

Foraminiferal geochemistry applies geochemical elements embedded in foraminiferal calcites through bioaccumulation to interpret and reconstruct past oceanic climate histories. Due to its extensive variability and abundance, foraminifera is the easiest to retrieve and the best indicator of marine productivity and ocean temporal changes. In this review, we discuss the development of foraminiferal geochemistry studies in Southeast Asia, analyzing its current status and potential areas to be developed, namely, the Sunda Shelf. The Sunda Shelf is one of the world’s largest low-latitude shelves, bordered by marginal seas and sensitive to sea-level changes. The shelf response towards changes in ocean salinity affected the isotopic signals in foraminiferal calcites, which can indicate sea-level changes ideally. The Sunda Shelf has the potential to be developed as a study area for eustatic sea-level changes as it is located far from major glaciation centers; hence through this review, we aim to highlight the potential of exploring the application of geochemical elements in foraminifera as an indicator for sea-level changes. To date, literature on foraminiferal geochemistry in this region is very limited, thus inhibiting progress in such studies. A comprehensive summary of past studies in this region is provided to give a general overview of the direction of foraminiferal geochemistry studies and serve as guidelines for future research. [ABSTRACT FROM AUTHOR]

The Strait of Malacca is one of the major shipping routes in naval logistics linking Indian and Pacific Oceans, which later these activities contributed to the trace metal accumulation in the Strait of Malacca. To assess the source of geochemical elements along with several factors affecting the concentrations in the surface sediments, five surface sediments were collected for physiochemical studies along the Strait of Malacca. The study revealed that the average of the clay, silt, and sand fraction was 10.93, 37.99, and 51.08 % respectively. The average concentrations of Al, Fe, Cr, Mn, and Mg, which were incorporated into seabed sediments through primary deposition from several sources were 5.88 ± 0.63 %, 2.78 ± 0.41 %, 5.73 x 10-3 ± 1.02 x 10-4 %, 9.32 x 10-3 ± 5.83 x 10-4 %, 4.72 x 10-2 ± 4.61 x 10-3 %, and 2.19 ± 0.21 % respectively. According to the results, the comparison of these elements with sediment quality guideline revealed that Cr contents were higher than the low range of the interim sediment quality guidelines (ISQG), suggesting that Cr may pose an environmental hazard. The average enrichment factor (EF) showed as minor and moderate enrichment for all elements while the contamination factor revealed that seabed sediments were affected by moderate level of Cr and Mg contamination. The pollution load indices (PLI) showed that only one sampling station N106 were affected by several sources of geochemical elements in its vicinity. Thus, the coastal area of Strait of Malacca may require further mitigation measure to contain the pollutant levels across the straits. [ABSTRACT FROM AUTHOR]

Sediment cores were collected from Kota Kinabalu and Labuan ports to determine the distribution of natural uranium isotopes, calcium (Ca), aluminium (Al) and total organic matter (TOM). A strong statistical correlation value between 234U/238U and Ca contents were shown at Kota Kinabalu (r 2 = 0.811), and Labuan (r ² = 0.833) ports. Good statistical correlation r 2 > 0.8 was also obtained between uranium isotopes and TOM at Kota Kinabalu port. Most activity ratio values of 234U/238U found in sediment cores from Kota Kinabalu port were more than 1.0; the major input of uranium at Kota Kinabalu port may be related to the sorptive process of authigenic uranium that occurs in the water column. In this case, the mobile U(VI) was reduced to immobile U(IV) by organic matter and scavenged to the sediment with co-precipitation of organic matter and calcium carbonate. On the other hand, a low activity ratio of 234U/238U (≤ 1) from Labuan was of detrital origin and also showed positive statistical correlation between calcium and aluminium. [ABSTRACT FROM AUTHOR]