Degradation rates and productivity signals of organic-walled dinoflagellate cyst species in surface sediment samples

To understand the role of the ocean within the global carbon cycle, detailed information is required on key-processes within the marine carbon cycle; bio-production in the upper ocean, export of the produced material to the deep ocean and the storage of carbon in oceanic sediments. Quantification of these processes requires the separation of signals of net primary production and the rate of organic matter decay as reflected in fossil sediments. This study examines the large differences in degradation rates of organic-walled dinoflagellate cyst species to separate these degradation and productivity signals. For this, accumulation rates of cyst species known to be resistant (R-cysts) or sensitive (S-cysts) to aerobic degradation of 62 sites are compared to mean annual chlorophyll-a, sea-surface temperature, sea-surface salinity, nitrate and phosphate concentrations of the upper waters and deep-water oxygen concentrations. Furthermore, the degradation of sensitive cysts, as expressed by the degradation constant k and reaction time t, has been related to bottom water [O2]. The studied sediments were taken from the Arabian Sea, north-western African Margin (North Atlantic), western-equatorial Atlantic Ocean/Caraibic, south-western African margin (South Atlantic) and Southern Ocean (Atlantic sector).
Significant relationships are observed between (a) accumulation rates of R-cysts and upper water chlorophyll-a concentrations, (b) accumulation rates of S-cysts and bottom water [O2] and (c) degradation rates of S-cysts (kt) and bottom water [O2].
Relationships that are extremely weak or are clearly insignificant on all confidence intervals are between (1) S-cyst accumulation rates and chlorophyll-a concentrations, sea-surface temperature (SST), sea-surface salinity (SSS), phosphate concentrations (P) and nitrate concentrations (N), (2) between R-cyst accumulation rates and bottom water [O2], SST, SSS, P and N, and between (3) kt and water depth. Co-variance is present between the parameters N and P, N, P and chlorophyll-a, oxygen and water depth. Correcting for this co-variance does not influence the significance of the relationship given above.
The possible applicability of dinoflagellate cyst degradation to estimate past net primary production and deep ocean ventilation is discussed.

为阐明海洋在全球碳循环中的作用，需获取海洋碳循环关键过程的详细数据：上层海洋生物生产、生源物质向深海的输出，以及碳在海洋沉积物中的埋藏。对上述过程的定量研究，需要区分净初级生产的信号与化石沉积物中反映的有机质降解速率。本研究聚焦于有机质壁沟鞭藻囊孢（dinoflagellate cyst）物种的降解速率差异，以此分离降解与生产力信号。

为此，本研究对比了62个站位中，对需氧降解具有抗性（R-囊孢）或敏感性（S-囊孢）的囊孢物种的堆积速率，与上层水域的年平均叶绿素a浓度、海表温度（sea-surface temperature, SST）、海表盐度（sea-surface salinity, SSS）、硝酸盐与磷酸盐浓度，以及底层水溶解氧浓度。此外，以降解常数k与反应时间t表征的敏感囊孢降解速率，已被证实与底层水溶解氧浓度相关。本次研究的沉积物样品取自阿拉伯海、西北非洲陆缘（北大西洋）、西赤道大西洋/加勒比海、西南非洲陆缘（南大西洋）以及南大洋大西洋扇区。

研究观测到三类显著相关关系：(a) R-囊孢堆积速率与上层水域叶绿素a浓度；(b) S-囊孢堆积速率与底层水溶解氧浓度；(c) S-囊孢降解速率（kt）与底层水溶解氧浓度。

在所有置信区间下相关性极弱或显著无关的关系包括：(1) S-囊孢堆积速率与叶绿素a浓度、海表温度（SST）、海表盐度（SSS）、磷酸盐浓度（P）及硝酸盐浓度（N）之间；(2) R-囊孢堆积速率与底层水溶解氧浓度、SST、SSS、P及N之间；以及(3) kt与水深之间。参数N与P、N、P与叶绿素a、溶解氧及水深之间存在协方差。对该协方差进行校正后，并不会影响前述相关关系的显著性。

本文还讨论了利用沟鞭藻囊孢降解速率估算过去净初级生产与深海通风状况的潜在适用性。