Elsevier

Marine Geology

Volume 429, November 2020, 106308
Marine Geology

Sedimentary records of bulk organic matter and lipid biomarkers in the Bering Sea: A centennial perspective of sea-ice variability and phytoplankton community

https://doi.org/10.1016/j.margeo.2020.106308Get rights and content

Highlights

  • Sediment OM may be related to primary productivity and regional depositional processes.

  • IP25 and PIP25 were used to confirm spatiotemporal variability in the formation of seasonal sea ice cover.

  • Recent coupled interactions of sea ice conditions and ecosystem responses were reconstructed.

  • Sea ice coverage was spatially heterogeneous in relation to phytoplankton community dynamics.

Abstract

In this study, organic geochemical analyses of two sediment cores (BL16 and LV63–23) recovered from the western Bering Sea were carried out to examine the sea-ice variability and its relationship to phytoplankton community evolution over the past century. Bulk stable organic carbon isotopic composition (δ13CTOC) showed pronounced depletion on the northern shelf since the late 1970s, indicating greater terrigenous organic matter (OM) under warming during recent decades. Variation in sedimentary OM in the southward core was closely associated with marine primary productivity and regional deposition processes. Arctic sea-ice proxy IP25 throughout the two cores with different temporal profile patterns demonstrated sea-ice presence with the spatio-temporal variability across the study area over the past century. The phytoplankton marker-IP25 index (PIP25), a proxy for estimating semi-quantitatively sea-ice concentrations, reflected a decreased sea-ice cover with more distinct interannual fluctuations between 0.7 and 0.2 (especially in core BL16) after the late 1970s, coinciding with the recent warming scenario. Increased concentrations of phytoplankton biomarkers (brassicasterol and dinosterol) and their ratios as well as the PIP25 record in core BL16 indicated a synchronous variability of reduced sea-ice cover with the enhancement of phytoplankton productivity since the late 1970s. These results suggested a coupled interaction of the sea-ice condition and planktonic ecosystem in the north Bering shelf. Our results also revealed recent (since the 2000s) spatial heterogeneity in sea-ice coverage between the northern and southern parts of the Bering Sea.

Introduction

The sub-Arctic Bering Sea, a transition region between the Pacific and Arctic Oceans, is a key area characterized by high productive and sensitive ecosystem dynamics (Grebmeier et al., 2006; Sigler et al., 2010). Due to its specific geographical location, seasonal sea-ice occurrence, high primary production and abundant biological resources, the Bering Sea plays an important role in the global carbon biogeochemical cycle with significant interaction and response to the recent climate change (e.g., Springer et al., 1996; Chen et al., 2002). Especially, the seasonal sea-ice coverage of the Bering Sea is a major driver of its ecology, which makes this ecosystem particularly sensitive to climate change (Guo et al., 2004; Sigler et al., 2010).

Over the past few decades, sea surface temperature (SST) has increased by about 3 °C in the Bering Sea (Stabeno et al., 2007, Stabeno et al., 2010), and the sea-ice cover has decreased in both concentration and duration (Stroeve et al., 2007, Stroeve et al., 2012). These recent changes have strongly impacted the ecosystem of the Bering Sea since the 1970s; rapid changes in the abundance of phytoplankton, zooplankton and fish have also been observed (Hunt et al., 2002). Recent changes in environmental condition, especially in the late 1970s, were closely associated with the well-documented 1976–1977 climate regime shift of the North Pacific, resulting in warming of the Bering Sea (Hare and Mantua, 2000; Bond et al., 2003). Numerous studies of the evolution of the Bering Sea ecosystem have focused on sea-ice loss connected with this regime shift, even its recognition is complicated by the presence of high-frequency, interannual variations in both physical and biological time series (e.g., Stabeno and Overland, 2001; Hunt et al., 2002; Wooster and Zhang, 2004; Overland and Stabeno, 2004; Stabeno et al., 2007). A dramatic increase in alkenones content around 2000 may have reflected changing hydrologic condition (e.g. stratification) in the northern Bering shelf (Harada et al., 2012); within the same period, annual sea-ice persistence started to increase dramatically in the southern Bering Sea (Frey et al., 2015), reflecting greater spatial heterogeneity in sea-ice variability (Brown and Arrigo, 2012; Frey et al., 2018). In spite of recent interannual variability especially towards the southern Bering Sea (Brown and Arrigo, 2012), considerable evidences has demonstrated that the long-term reduction in sea-ice cover has caused concomitant ecosystem change in the Bering Sea (e.g., Hunt et al., 2002; Grebmeier et al., 2006). Therefore, the Bering Sea is thought to have experienced significant environmental changes under climate warming within the Pacific Arctic region (e.g., Grebmeier et al., 2006; Stroeve et al., 2007; Giesbrecht et al., 2019; Cornwall, 2019).

The sea-ice cover is a critical component of the Bering Sea ecosystem; its seasonal variability is extremely sensitive to changes in both weather and climate (e.g., Overland, 1981; Brown and Arrigo, 2012). The duration and extent of sea ice, sea water temperature and water mass structures are critical controls of the ecosystem dynamics in the Pacific Arctic (Grebmeier et al., 2006). Ecosystem changes in the Bering Sea during recent decades have commonly been attributed to earlier sea-ice retreat and regional atmospheric–oceanic forcing (e.g. the Aleutian Low and sea-water warming) (Grebmeier et al., 2006). Long-term shifts towards earlier algal growth have also been observed, which indicates an ongoing ecosystem shift in this high-latitude marine ecosystem (Fietzke et al., 2015).

Climate-driven regional regime shifts have been reported in the northern Pacific, with potential linkages to environmental changes at interannual or seasonal timescales (Stabeno et al., 1999). However, few studies have coupled a long-term regional climate change with corresponding primary productivity and community structure and their responses, especially in the western Bering Sea. The lack of in situ observations over decadal timescales makes it impossible to identify long-term changes in primary production in this highly productive but sensitive Pacific Arctic region (Hill et al., 2018). Accordingly, analyses of decadal sediment records using sea-ice indicators and phytoplankton-based biomarkers may facilitate the evaluation of the change towards the evolution and/or shifting of phytoplankton community and their relationship to the sea-ice variation.

In recent decades, the organic geochemical biomarker IP25, a highly branched, monounsatuarated C25 isoprenoid (HBI) alkene derived from sea ice diatoms, has been developed as sea ice proxy (Belt et al., 2007). IP25 as well as the so-called PIP25 (Phytoplankton-IP25) have subsequently been used to reconstruct recent and past sea-ice conditions in Arctic and sub-Arctic regions (e.g., Müller et al., 2009, Müller et al., 2011; Fahl and Stein, 2012; Méheust et al., 2013; Xiao et al., 2013, Xiao et al., 2015; Belt et al., 2015; Stein et al., 2016; Ruan et al., 2017; Bai et al., 2019; for reviews see Stein et al., 2012; Belt and Müller, 2013; Belt, 2018). In the Chukchi/Bering Sea area, i.e., a region close to our study area, IP25 and phytoplankton biomarker records reflecting the Last Glacial and Holocene history of sea-ice and primary productivity are published by Méheust et al., 2015, Méheust et al., 2018, Polyak et al. (2016) and Stein et al. (2017).

In the present study, we analyzed these biomarkers in two sediment cores well-dated in 210Pb from the western Bering Sea to determine a long-term phytoplankton community evolution and biomarker-related sea-ice occurrence over the past century. The main objectives were to examine long-term sea-ice conditions and phytoplankton evolution, and to identify the relationships between the sea-ice conditions and phytoplankton productivity as well as its spatial variability in the context of the recent climate regime shifts in the Bering Sea.

Section snippets

Regional setting

The Bering Sea, which is characterized by seasonal variation in sea-ice coverage, is the gateway for the imports from the Pacific Ocean to the Arctic Ocean (Jones et al., 2003). The physical oceanography of the Bering Sea is influenced by tides, winds, topography, flows through passages and the annual formation, drift and melting of sea ice (Schumacher et al., 2003). In summer, three major water masses flow northward over the northern Bering shelf (Fig. 1). On this shallow shelf, the Alaska

Sampling and sediment core dating

Two sediment cores (BL16 and LV63–23) were recovered from the Bering Sea during the 2012 Chinese Arctic Research Expedition (CHINARE-2012) and the 2013 China-Russia Joint Expedition, respectively, using a multicorer (Fig. 1). The two cores were subsampled at 1 cm intervals and then stored at −20 °C until further processing.

Sedimentation rates and the chronology framework were determined for each core by analyzing 210Pb and 137Cs activity in selected horizons (Fig. 2). Age model for each of the

210Pb and 137Cs profiles and sediment chronology of the two cores

Profiles of excess 210Pb (210Pbex) in the two cores are shown in Fig. 2 and linear sediment rates were calculated based on the constant initial concentration (CIC) model according to the exponential decreased trend of 210Pbex throughout the core (Fig. 2). The log-linear 210Pbex profiles coupled with steady sediment composition throughout the two cores indicated limited bioturbation or sediment disturbance, although a few vertically homogeneous trends were visible in the upper horizons (e.g.,

Source identification of sedimentary organic matter (SOM)

The low TOC/TN ratios observed in core BL16 (5.86 ± 0.49, Table S2) from the northern shelf may be partly related to the presence of soil-derived bound ammonium due to adsorption by clays, causing (too) low ratios (Schubert and Calvert, 2001; Stein and Macdonald, 2004). This finding is also in line with the previous reports of OM sources along the high-latitude coastal margins of the southern Chukchi Sea, which showed more refractory OM near shore versus more labile OM at offshore and/or in the

Conclusions

Sedimentary bulk organic matter and biomarker records indicated decadal to centennial timescales of sea-ice variability across the Bering Sea and corresponding phytoplankton community changes in this sensitive Pacific Arctic region. A trend of δ13CTOC depletion since the late 1970s observed in the core sampled from the northern Bering shelf revealed increased terrigenous input, which could be ascribed to warming scenario during recent decades. Compared to the northern shelf, where OM

Declaration of Competing Interest

None.

Acknowledgments

We wish to thank the participants of R/V Xuelong and R/V Akademik M.A. Lavrentyev for sampling assistance during the cruise. We are most grateful to members of the AWI laboratory (Lester Lembke-Jene and Nicoletta Ruggieri) and the Kochi University (Minoru Ikehara) for help with sample processing and organic chemical analysis. This work was financially supported by Qingdao National Laboratory for Marine Science and Technology (2016ASKJ13, 2018SDKJ0104-3), the National Natural Science Foundation

References (101)

  • K.E. Frey et al.

    Divergent patterns of recent sea ice cover across the Bering, Chukchi, and Beaufort seas of the Pacific Arctic Region

    Prog. Oceanogr.

    (2015)
  • K. Giesbrecht et al.

    A decade of summertime measurements of phytoplankton biomass, productivity and assemblage composition in the Pacific Arctic Region from 2006 to 2016

    Deep-Sea Res. II Top. Stud. Oceanogr.

    (2019)
  • L. Guo et al.

    Distributions, speciation and stable isotope composition of organic matter in the southeastern Bering Sea

    Mar. Chem.

    (2004)
  • S.R. Hare et al.

    Empirical evidence for North Pacific regime shifts in 1977 and 1989

    Prog. Oceanogr.

    (2000)
  • V. Hill et al.

    Decadal trends in phytoplankton production in the Pacific Arctic Region from 1950 to 2012

    Deep-Sea Res. II Top. Stud. Oceanogr.

    (2018)
  • L. Hu et al.

    Sources, dispersal and preservation of sedimentary organic matter in the Yellow Sea: the importance of depositional hydrodynamic forcing

    Mar. Geol.

    (2013)
  • T. Iida et al.

    Temporal and spatial variability of chlorophyll concentrations in the Bering Sea using empirical orthogonal function (EOF) analysis of remote sensing data

    Deep-Sea Res. II Top. Stud. Oceanogr.

    (2007)
  • K. Matsumoto et al.

    Association of picophytoplankton distribution with ENSO events in the equatorial Pacific between 145°E and 160°W

    Deep-Sea Res. I Oceanogr. Res. Pap.

    (2004)
  • I. McCave

    Local and global aspects of the bottom nepheloid layers in the world ocean

    Neth. J. Sea Res.

    (1986)
  • M. Méheust et al.

    Variability in modern sea surface temperature, sea ice and terrigenous input in the sub-polar North Pacific and Bering Sea: Reconstruction from biomarker data

    Org. Geochem.

    (2013)
  • K. Mizobata et al.

    Variability of Bering Sea eddies and primary productivity along the shelf edge during 1998–2000 using satellite multisensor remote sensing

    J. Mar. Syst.

    (2004)
  • K. Mizobata et al.

    Bering Sea cyclonic and anticyclonic eddies observed during summer 2000 and 2001

    Prog. Oceanogr.

    (2002)
  • J. Müller et al.

    Towards quantitative sea ice reconstructions in the northern North Atlantic: a combined biomarker and numerical modelling approach

    Earth Planet. Sci. Lett.

    (2011)
  • K. Nagashima et al.

    Contribution of detrital materials from the Yukon River to the continental shelf sediments of the Bering Sea based on the electron spin resonance signal intensity and crystallinity of quartz

    Deep-Sea Res. II Top. Stud. Oceanogr.

    (2012)
  • A. Naidu et al.

    Stable organic carbon isotopes in sediments of the north Bering-south Chukchi seas, Alaskan-Soviet Arctic Shelf

    Cont. Shelf Res.

    (1993)
  • H. Niebauer et al.

    A time-series study of the spring bloom at the Bering Sea ice edge I. Physical processes, chlorophyll and nutrient chemistry

    Cont. Shelf Res.

    (1995)
  • K. Oguri et al.

    Excess 210Pb and 137Cs concentrations, mass accumulation rates, and sedimentary processes on the Bering Sea continental shelf

    Deep-Sea Res. II Top. Stud. Oceanogr.

    (2012)
  • S.R. Okkonen et al.

    Satellite and hydrographic observations of the Bering Sea ‘Green Belt’

    Deep-Sea Res. II Top. Stud. Oceanogr.

    (2004)
  • S. Rodionov et al.

    The Aleutian Low, storm tracks, and winter climate variability in the Bering Sea

    Deep-Sea Res. II Top. Stud. Oceanogr.

    (2007)
  • J. Ruan et al.

    Holocene variability in sea surface temperature and sea ice extent in the northern Bering Sea: a multiple biomarker study

    Org. Geochem.

    (2017)
  • S. Schmidt et al.

    Sedimentary processes in the Thau Lagoon (France): from seasonal to century time scales

    Estuar. Coast. Shelf Sci.

    (2007)
  • C.J. Schubert et al.

    Nitrogen and carbon isotopic composition of marine and terrestrial organic matter in Arctic Ocean sediments:: implications for nutrient utilization and organic matter composition

    Deep-Sea Res. I Oceanogr. Res. Pap.

    (2001)
  • P. Stabeno et al.

    On the recent warming of the southeastern Bering Sea shelf

    Deep-Sea Res. II Top. Stud. Oceanogr.

    (2007)
  • P. Stabeno et al.

    Factors influencing physical structure and lower trophic levels of the eastern Bering Sea shelf in 2005: Sea ice, tides and winds

    Prog. Oceanogr.

    (2010)
  • P.J. Stabeno et al.

    Comparison of warm and cold years on the southeastern Bering Sea shelf and some implications for the ecosystem

    Deep-Sea Res. II Top. Stud. Oceanogr.

    (2012)
  • C.-C. Su et al.

    210Pb, 137Cs and 239,240 Pu in East China Sea sediments: sources, pathways and budgets of sediments and radionuclides

    Mar. Geol.

    (2002)
  • S. Takeda et al.

    Biological and chemical characteristics of high-chlorophyll, low-temperature water observed near the Sulu archipelago

    Deep-Sea Res. II Top. Stud. Oceanogr.

    (2007)
  • K.R. Wood et al.

    A decade of environmental change in the Pacific Arctic region

    Prog. Oceanogr.

    (2015)
  • W.S. Wooster et al.

    Regime shifts in the North Pacific: early indications of the 1976–1977 event

    Prog. Oceanogr.

    (2004)
  • X. Xiao et al.

    Biomarker distributions in surface sediments from the Kara and Laptev seas (Arctic Ocean): indicators for organic-carbon sources and sea-ice coverage

    Quat. Sci. Rev.

    (2013)
  • X. Xiao et al.

    Sea-ice distribution in the modern Arctic Ocean: biomarker records from trans-Arctic Ocean surface sediments

    Geochim. Cosmochim. Acta

    (2015)
  • A.M. Aguilar-Islas et al.

    Sea ice-derived dissolved iron and its potential influence on the spring algal bloom in the Bering Sea

    Geophys. Res. Lett.

    (2008)
  • N.J. Anderson

    Diatoms, temperature and climatic change

    Eur. J. Phycol.

    (2000)
  • K.R. Arrigo et al.

    Impact of a shrinking Arctic ice cover on marine primary production

    Geophys. Res. Lett.

    (2008)
  • S.T. Belt

    Source-specific biomarkers as proxies for Arctic and Antarctic Sea ice

    Org. Geochem.

    (2018)
  • N. Bond et al.

    Recent shifts in the state of the North Pacific

    Geophys. Res. Lett.

    (2003)
  • Z.W. Brown et al.

    Contrasting trends in sea ice and primary production in the Bering Sea and Arctic Ocean

    ICES J. Mar. Sci.

    (2012)
  • Z.W. Brown et al.

    Sea ice impacts on spring bloom dynamics and net primary production in the Eastern Bering Sea

    J. Geophys. Res.: Oceans

    (2013)
  • Z.W. Brown et al.

    A reassessment of primary production and environmental change in the Bering Sea

    J. Geophys. Res.: Oceans

    (2011)
  • B. Chen

    Patterns of thermal limits of phytoplankton

    J. Plankton Res.

    (2015)
  • View full text