Unraveling Historical Carbon Records of <i>Zostera marina</i> Seagrass Meadows: High‐Resolution Analysis, Dating, and Methodological Evaluation of Deep Sediment Cores

Abstract Understanding long‐term carbon storage in temperate seagrass habitats is crucial for assessing their role as a “nature‐based” climate solution. However, many studies often use shallow cores, low‐resolution analyses, and inconsistent methodologies, limiting the ability to infer large‐scale carbon storage potential. This study presents the first high‐resolution carbon analysis of temperate seagrass sediments to 3 m depth and provides first estimates of sediment and carbon accumulation rates for UK subtidal meadows. Three sediment vibrocores were collected from a subtidal Zostera marina meadow at Drakes Island, Plymouth Sound, UK. High‐resolution sampling at 1 cm intervals in the upper meter, and every 5 cm thereafter, enabled detailed analysis of organic carbon (%OC), calcium carbonate, and particle size, with microscope observations recorded. Several methods for %OC analysis were compared, and 210 Pb dating was used to determine accumulation rates. OC content varied widely (0.24%–27.55%), yielding variable mean OC stocks of 302.34 ± 197.44 Mg C ha −1 over the upper meter. Exceptionally high OC peaks were attributed to coal layers in the sediment. Estimated sediment and carbon accumulation rates ranged from 0.19 to 0.27 g cm −2 yr −1 and 0.32 to 0.45 Mg C ha −1 yr −1 , indicating potential core ages up to 1,300 years. Findings highlight the importance of high‐resolution, multi‐proxy analysis to assess long‐term carbon storage and provided valuable historical insights. This study shows how methodological inconsistencies can lead to inaccurate stock estimates, emphasizing the need for standardization. Addressing these issues aids the advancement of accurate carbon storage quantification, provides valuable storage rate data for management, and strengthens future seagrass carbon research.