Publication Date:
2019-06-17
Description:
Phytoplankton productivity and community structure in the East China Sea (ECS) play an important role in
marine ecology and carbon cycle, but both have been changing rapidly in response to recent oceanic and atmospheric
circulation changes. However, the lack of long-term records of phytoplankton productivity and
community structure variability in the region hinders our understanding of natural forcing mechanisms. Here,
we use the phytoplankton biomarker (brassicasterol, dinosterol and alkenones) contents as well as the ratios
between these biomarkers in three sediment cores from the ECS shelf to reconstruct the spatiotemporal variations
of productivity and community of diatoms, dinoflagellates and coccolithophores during the Holocene,
respectively. During 9–7 ka, the ECS shelf was characterized by low phytoplankton productivity with low coccolithophore
contribution, caused by the oligotrophic condition mainly owing to the restricted Kuroshio Current
(KC) intrusion under low sea-level conditions, thus the lack of nutrient input. Phytoplankton productivity
generally increased during 7–4.6 ka, in response to the initial intrusion of the Yellow Sea Warm Current (YSWC,
a branch of the KC), bringing nutrient from the subsurface KC to the upper layer of the ECS for phytoplankton
growth. Phytoplankton productivity continuously increased during 4.6–1 ka, due to an enhanced circulation
system (YSWC and Yellow Sea Coastal Current (YSCC)) driven by strong East Asia Winter Monsoon (EAWM).
Significantly, high alkenone contents and coccolithophore contribution in the eastern core F11A was associated
with its location closer to the warm and saline YSWC, which was suitable for coccolithophore growth. Beyond
diagenetic processes which could partly account for higher biomarker contents near core tops, elevated phytoplankton
productivity during the last 1 ka might be induced by more nutrient supply from the intensified
circulation system driven by enhanced KC and anthropogenic activities. The latter also resulted in high dinoflagellate
proportions in all three cores. These temporal and spatial changes of phytoplankton productivity and
community structure in the ECS during the Holocene corresponded to different mechanisms by the air-sea interaction,
providing insights into distinguishing natural forcing and anthropogenic influences on marine ecology.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
isiRev
Format:
application/pdf
Permalink