Response of Mangrove Development to Air Temperature Variation Over the Past 3000 Years in Qinzhou Bay, Tropical China

Zhen Li,Peng Xia,Yao Zhang,Xianwei Meng

doi:10.3389/feart.2021.678189

Abstract

Mangroves, a blue carbon ecosystem between land and ocean in the (sub)tropics, are sensitive to changes in climate and the sea level. It is imperative to reconstruct the historical dynamics of their development to predict the fate of mangrove ecosystems in the backdrop of rapid global changes. This study analyzes records of the sources of organic matter from sediment core Q43 of Qinzhou Bay in tropical China by using the endmember mixing model based on stable organic carbon isotopes and C/N ratio. Mangrove-derived organic matter (MOM) is regarded as a reliable indicator for reconstructing the historical development of mangroves. The variations in MOM in Qinzhou Bay over the past ∼3,000 cal yr BP indicate that mangrove forests underwent two periods of flourishment: ∼2,200–1,750 cal yr BP and ∼1,370–600 cal yr BP, as well as three periods of deterioration: ∼3,000–2,200 cal yr BP, ∼1,750–1,370 cal yr BP, and ∼600–0 cal yr BP. Of factors that might have been influential, changes in the relative sea level and the regional hydrological environment (e.g., seawater temperature, salinity, and hydrodynamic conditions) did not appear to have notable effects on mangrove flourishing/degradation. However, climate change, especially the variation in air temperature, formed the primary factor controlling mangrove development. The stages of mangrove flourishing/deterioration corresponded to the warm/cold periods of the climate, respectively. Noteworthy is that the rapid rise in air temperature during the Anthropocene warm period should have promoted mangrove development, but the increasing intensity of human activity has reversed this tendency leading to the degradation of mangroves.

Highlights

Mangroves inhabit intertidal zones in tropical and subtropical regions, and control exchanges of materials at the interfaces of the land, marine, and atmosphere ecosystems (Woodroffe et al, 2016; Hatje et al, 2020)
Our results show that stages of relatively negative excursion of δ18O (∼2,200–1,750 and ∼1,370–600 cal yr BP) correspond to the periods of mangrove flourishing (Stage 2 and Stage 4), while sections with positive δ18O (∼1,750–1,370 and ∼600–200 cal yr BP) correspond to the periods of mangrove deterioration (Stage 3 and early Stage 5)
Our results show that the three periods of mangrove deterioration approximately correspond to the Zhou Dynasty cold period (ZDCP), WJCP, and MQCP, whereas the two periods of mangrove flourishing approximately correspond to the Qin-Han warm period (QHWP) and Sui-Tang warm period (STWP)-SYWP, respectively (Figure 5)

Summary

Introduction

Mangroves inhabit intertidal zones in tropical and subtropical regions, and control exchanges of materials at the interfaces of the land, marine, and atmosphere ecosystems (Woodroffe et al, 2016; Hatje et al, 2020). They provide multiple ecosystem services, such as mitigating coastal erosion from waves and wind, guaranteeing fishery resources and food security for coastal inhabitants, and aiding. Anthropogenic threats, such as pollution, overexploitation, and the conversion of patterns of land use (Bao et al, 2013; Friess et al, 2019; Veettil et al, 2019), have vastly impacted mangrove dynamics, especially since the Anthropocene

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Discussion

Conclusion