Sediment characteristics ofdifferent coastal ecosystems along the Central eastern Red Sea coast and western Arabian Gulf, supplement to: Saderne, Vincent; Cusack, Michael; Almahasheer, Hanan; Serrano, Óscar; Masqué, Pere; Arias-Ortiz, Ariane; Krishnakuma

The dataset content the 14C and 210Pb geochronologies of mangroves, seagrass and saltmarshes of the Central eastern red sea coast and western Arabian Gulf.It also content depth profiles of CaCO3 content in the sediments of these ecosystems as well as the calculated burial rates in those sediments.A total of 52 cores were sampled along 80 km coastline of the Kingdom of Saudi Arabia in the central Red Sea (2015) and the Arabian Gulf (2016) (29 in mangroves forests and 23 in seagrass meadows, table 1). Seagrass soil cores were sampled in 1 to 4 m deep seagrass meadows, dominated by Halophila sp., Thalassia hemprichii, Enhalus acoroides, Thalassodendrum ciliatum and Cymodeacea sp., and mangrove soil cores were sampled in intertidal mono-specific A. marina forests. The sites sampled in the Red Sea include the coastal island of Al Taweelah (22°16'N, 39°05'E; 8 mangrove and 3 seagrass coring locations) and 3 coastal lagoons: Khor Almesena'a (22°22'N, 39°07'E; 8 mangroves and 10 seagrass coring locations), Khor Al-Baqila (22°44'N, 39°00'E; 6 coring locations in mangroves) and Khor Al-Kharrar (22°57'N, 38°51'E; 7 coring locations in mangroves and 10 in seagrasses) (Fig 1). Khor Al-Baqila underwent a major alteration with the conversion of the entire southern side of the embayment into a petrochemical terminal starting in 1981. Similarly, an important development of hard engineering structures occurred in the shoreline in front of Al Taweelah Island in the early 2010's .We also sampled 25 cores in the Saudi Arabian coast of the Arabian Gulf at 4 sites, Ras Safaniya (27°58'N, 48°46'E), Abu Ali Island (27°17' N, 49°33' E), Ras Tanura - Safwa (26°41' N, 50°00' E) and Uqair (25°43' N, 50°13' E) (Fig. 1). Three seagrass cores were sampled at each location in Halodule uninervis and Halophila stipulacea meadows (total of 12 cores). Additionally, 3 mangrove and 3 sabkha cores were sampled in the south of Abu Ali Island and 4 mangrove cores and 3 sabkha cores were sampled in the area of Ras Tanura - Safwa (Fig 1). All sites except Uqair have underwent alterations associated with the prevalent industrial and urban development in the region since the 1950s, including land reclamation, dredging, construction of bridges and pipelines, and oil spills.Soil cores were sampled using manual percussion and rotation (PVC pipe with an inner diameter of 70 mm). The length of core barrel inserted into the soil and the length of retrieved soil was recorded in order to correct for compression effects following the guidelines of Howard et al. (2014). All variables studied here are referenced to the corrected, uncompressed depths. The cores were sealed at both ends, transported vertically and stored at 4 °C before processing in the laboratory.2.3 Biogeochemical analysisThe soil cores were segmented into 1-cm-thick slices, which were oven-dried at 60 °C until constant weight to determine the dry bulk density (g cm-3). The slices were then grounded in an agate mortar and subdivided for analysis. All depths were corrected for compression considering a uniform distribution of the compaction throughout the total length of the cores as described by Serrano et al. (2016b). The mean ± SE compression factors (depth ratio between compressed and uncompressed soil) were 1.05 ± 0.18, 1.04 ± 0.03 and 1.16 ± 0.11 in the cores from sabkha, mangrove and seagrass sites of the Arabian Gulf respectively, and 1.19 ± 0.14 and 1.23 ± 0.17 in the seagrass and mangrove cores of the Red Sea.Short-term (last decades - century) and long-term (millennia) soil chronologies were established using 210Pb and 14C analyses, respectively. Forty-five cores were analyzed to retrieve chronologies using the 210Pb technique, 20 cores from the Red Sea (9 in seagrass and 11 in mangroves) and 25 cores from the Arabian Gulf (7 in mangroves, 12 in seagrass and 6 in sabkhas). The activity concentrations of 210Pb in the upper 20 to 30 cm (compressed) were determined in the soil fraction