鄱阳湖地区过去2160年孢粉记录的植被变化及影响因素

本研究在AMS ¹⁴C测年的基础上,通过分析鄱阳湖430 cm沉积剖面44个样品的孢粉记录和有机碳（TOC）指标,同时结合江西人口密度指标及当地历史文献资料,重点探讨了该区过去2160年植被变化的影响因素及在人类活动影响下该区域植被变化的历史。研究结果显示,鄱阳湖流域过去2160年植被变迁及人类活动变化主要分为5个阶段：1）160 BC~400 A.D.,乔灌木花粉含量较低,草本植物花粉较高,指示鄱阳湖流域周围地势低平的地带已经被广泛垦殖,但周围仍分布着一定量的常绿阔叶类、落叶阔叶类以及针叶类植被。高含量的禾本科表明鄱阳湖流域的稻作农业已初具规模,但该期乔灌木花粉含量相对较高,蕨类孢子含量较低,人口密度较小,指示该时期森林覆盖度较高,人类活动相对较弱。2）400~800 A.D.,乔灌木植物花粉与草本植物含量变化不大,植被与前期基本一致。高含量的蕨类孢子指示人类活动进一步加强,但人口密度较低,指示该时期森林覆盖度仍然较高,人类活动相对较弱。3）800~1350 A.D.,乔灌木花粉含量显著下降,而与人类活动相关的草本植物花粉含量略有上升,表明鄱阳湖流域随着人类活动增强,地带性森林植被遭受到一定的破坏,森林覆盖度明显下降,该期人口密度迅速递增,农业垦殖强度进一步加强,农业生产规模继续扩大,指示该时期人类活动影响较强,森林植被覆盖度较低。4）1350~1650 A.D.,乔灌木花粉含量略有上升,草本植物花粉含量略有下降,指示该时期鄱阳湖流域常绿阔叶类、落叶阔叶类及针叶类植被较前期略有恢复,尤其是松属花粉含量增长明显,表明该区地带性植被破坏后逐渐演变为具有次生性质的松林。该时期由于气候变冷,自然灾害频发,加上战争频繁,人口密度显著下降,人类活动影响减弱,进而导致森林植被略有恢复。5）1650 A.D.至今,鄱阳湖流域植被与前期较为一致,但松属花粉含量后期呈现明显的下降趋势,表明鄱阳湖流域随着人类活动进一步加强,次生松林破坏较为严重。过去2000多年气候变化虽然对区域植被有一定的影响,但历史时期以来人口的不断增长、农业的快速发展以及国家鼓励农民垦荒政策的实施是引起当地森林植被减少以及生态环境退化的主要原因,该结果对鄱阳湖流域恢复和重建自然生态环境具有重要的理论价值。

     

Composition,abundance, biomass,and production of macrofauna in a New England estuary: Comparisons among eelgrass meadows and other nursery habitats

Quantitative suction sampling was used to characterize and compare the species composition, abundance, biomass, and secondary production of macrofauna inhabiting intertidal mud-flat and sand-flat, eelgrass meadow, and salt-marsh-pool habitats in the Nauset Marsh complex, Cape Cod, Massachusetts (USA). Species richness and abundance were often greatest in eelgrass habitat, as was macroinvertebrate biomass and production. Most striking was the five to fifteen times greater rate of annual macrofaunal production in eelgrass habitat than elsewhere, with values ranging from approximately 23–139 g AFDW m² yr^?1. The marsh pool containing widgeon grass (Ruppia maritima) supported surprisingly low numbers of macroinvertebrates, probably due to stressfully low dissolved oxygen levels at night during the summer. Two species of macroinvertebrates, blue mussels (Mytilus edulis) and to a lesser extent bay scallops (Argopecten irradians), used eelgrass as “nursery habitat.” Calculations showed that macroinvertebrate production is proportionally much greater than the amount of primary production attributable to eelgrass in the Nauset Marsh system, and that dramatic changes at all trophic levels could be expected if large changes in seagrass abundance should occur. This work further underscores the extraordinarily large impact that seagrass can have on both the structure and function of estuarine ecosystems. *** DIRECT SUPPORT *** A01BY070 00006     

白洋淀近80年生态环境变化的硅藻记录

白洋淀是雄安新区实现"以水定城"理念的关键,了解其生态变化轨迹及特征有望为白洋淀的治理提供科学参考依据。本文基于取自白洋淀东南部湖区的一根长79 cm的沉积岩芯,分析该岩芯的硅藻记录并结合沉积物地球物理和化学指标、气象监测数据及人类活动指标,重建了该湖区近80年的硅藻属种组合及多样性变化过程和特征并探讨其变化机制。研究结果表明,Achnanthidium minutissimum、Amphora copulata、Puncticulata praetermissa、Pantocsekiella ocellata和Cyclotella distinguenda是沉积硅藻群落的优势种。本研究分析的物种多样性指数包括物种丰富度、均匀度和β多样性指数（βsor）。其中,物种丰富度和均匀度呈总体上升趋势,βsor呈总体下降趋势,说明过去80年硅藻属种数量净获得量增加,但硅藻群落结构变化趋于均匀化。冗余分析（RDA）和变差分解（VPA）显示气候和人类活动因子对硅藻属种组合和多样性变化产生了不同程度的影响,其中年均温、湖水位和沉积物P元素含量的贡献较大。年均温对硅藻属种组合变化的独立解释百分比最大,说明未来气候持续变暖的条件下,气温对白洋淀生态系统的影响可能会增强。湖水位对硅藻多样性变化的贡献最大,说明维持生态需水量对保护白洋淀生物多样性的重要性。基于普通最小二乘法残差的累积和（OLS-CUSUM）未检测出硅藻属种组合和多样性存在突变点,说明过去几十年人类活动和气候变化尚未造成该湖区生态系统稳态的转化。因此,减轻环境压力有望保持该湖区生态系统的恢复力和稳定性。但对于重污染湖区,其硅藻优势种和属种组合变化与本研究湖区存在很大差异,需进一步研究以获得更具针对性的水环境治理对策。     

Sedimentary evolution and environmental history of Lake Van (Turkey) over the past 600 000 years

The lithostratigraphic framework of Lake Van, eastern Turkey, has been systematically analysed to document the sedimentary evolution and the environmental history of the lake during the past ca 600 000 years. The lithostratigraphy and chemostratigraphy of a 219 m long drill core from Lake Van serve to separate global climate oscillations from local factors caused by tectonic and volcanic activity. An age model was established based on the climatostratigraphic alignment of chemical and lithological signatures, validated by ⁴⁰Ar/³⁹Ar ages. The drilled sequence consists of ca 76% lacustrine carbonaceous clayey silt, ca 2% fluvial deposits, ca 17% volcaniclastic deposits and 5% gaps. Six lacustrine lithotypes were separated from the fluvial and event deposits, such as volcaniclastics (ca 300 layers) and graded beds (ca 375 layers), and their depositional environments are documented. These lithotypes are: (i) graded beds frequently intercalated with varved clayey silts reflecting rising lake levels during the terminations; (ii) varved clayey silts reflecting strong seasonality and an intralake oxic–anoxic boundary, for example, lake‐level highstands during interglacials/interstadials; (iii) CaCO₃‐rich banded sediments which are representative of a lowering of the oxic–anoxic boundary, for example, lake level decreases during glacial inceptions; (iv) CaCO₃‐poor banded and mottled clayey silts reflecting an oxic–anoxic boundary close to the sediment–water interface, for example, lake‐level lowstands during glacials/stadials; (v) diatomaceous muds were deposited during the early beginning of the lake as a fresh water system; and (vi) fluvial sands and gravels indicating the initial flooding of the lake basin. The recurrence of lithologies (i) to (iv) follows the past five glacial/interglacial cycles. A 20 m thick disturbed unit reflects an interval of major tectonic activity in Lake Van at ca 414 ka bp . Although local environmental processes such as tectonic and volcanic activity influenced sedimentation, the lithostratigraphic pattern and organic matter content clearly reflect past global climate changes, making Lake Van an outstanding terrestrial archive of unprecedented sensitivity for the reconstruction of the regional climate over the last 600 000 years.     

Timing and cause of water level fluctuations in Kluane Lake, Yukon Territory, over the past 5000 years

We reconstructed late Holocene fluctuations of Kluane Lake in Yukon Territory from variations in bulk physical properties and carbon and nitrogen elemental and isotopic abundances in nine sediment cores. Fluctuations of Kluane Lake in the past were controlled by changes in climate and glaciers, which affected inflow of Slims and Duke rivers, the two largest sources of water flowing into the lake. Kluane Lake fluctuated within a narrow range, at levels about 25 m below the present datum, from about 5000 to 1300 cal yr BP. Low lake levels during this interval are probably due to southerly drainage of Kluane Lake to the Pacific Ocean, opposite the present northerly drainage to Bering Sea. Slims River, which today is the largest contributor of water to Kluane Lake, only rarely flowed into the lake during the period 5000 to 1300 cal yr BP. The lake rose 7-12 m between 1300 and 900 cal yr BP, reached its present level around AD 1650, and within a few decades had risen an additional 12 m. Shortly thereafter, the lake established a northern outlet and fell to near its present level.     

Modeling the response of water quality in the Seine River estuary to human activity in its watershed over the last 50 years

The unique database of water quality measurements made in the Seine estuary over 45 years by the Service de la Navigation de la Seine at Rouen is used here to reconstruct the evolution of oxygen status in the estuary and the nutrient fluxes to the Seine Bight during the last half century. The Riverstrahler model is used to establish the link between these long-term trends in the functioning of the Seine system and the evolution of agricultural, domestic, and industrial activity in the watershed over this period taking into account natural and man-induced hydrological variations. Oxygenation of the fluvial sector below Paris has increased considerably owing to improved wastewater treatment, but a large part of the estuary remains completely anoxic during the spring and summer months. Nitrogen input to surface waters from urban sources has remained essentially constant while diffuse inputs from agricultural soils have increased 5-fold as a result of more intensive agricultural practices as well as the loss of retention capacity in riparian zones. Phosphorus inputs from domestic and industrial sources increased 3-fold from 1950 to 1980, but have decreased gradually in recent years. The generally high level of phosphorus contamination has favored strong algal development in all large tributaries of the Seine River upstream of paris since the 1960s. Silica inputs, originating mainly from the weathering of rocks, fluctuate widely depending on hydrology. In-stream retention of silica, linked to diatom blooms, has increased but remains limited. These changes have induced several shifts in the nutrient limitation conditions of the Seine Bight.     

1956—2008年鄱阳湖流域水沙输移趋势及成因分析

利用鄱阳湖流域代表性水文站1956—2008年实测年径流量及年输沙量资料序列,采用Mann-Kendall秩相关检验法,研究鄱阳湖流域水沙量年际变化趋势和可能发生突变的时间,并从流域降雨、用水、水库拦沙、水土流失及其治理等方面分析了鄱阳湖流域水沙变化的主要影响因素。研究结果表明:鄱阳湖地区来水量和出湖水量有小幅增大趋势;鄱阳湖流域来沙量呈异常显著减小趋势,发生突变的年份为1998—1999年;实测出湖沙量从2002年开始呈明显的减少趋势。通过对有关影响因素的研究,发现鄱阳湖流域气候变化降雨量减少对近10年鄱阳湖出入湖径流量的减少影响显著;水库滞沙是鄱阳湖入湖沙量减少的主要原因;出湖沙量变化主要受上游水库群的影响,还有近年湖区采砂的影响。     

Long-term declines in two apex predators,bull sharks (<Emphasis Type="Italic">Carcharhinus leucas</Emphasis>) and alligator gar (<Emphasis Type="Italic">Atractosteus spatula</Emphasis>), in Lake Pontchartrain,an oligohaline estuary in southeastern Louisiana

We analyzed historic and current fishery independent data to determine if the abundance of two apex predators, bull sharks (Carcharhinus leucas) and alligator gar (Atractosteus spatula), in Lake Pontchartrain had changed significantly over the last half century. Lake Pontchartrain is an environmentally degraded oligohaline estuary in southeastern Louisiana that has experienced considerable changes in fish assemblage composition over this interval. Using gillnet, beach seine, and trawl data collected during three time periods (1953–1955, 1977–1978, and 1996–2005), we analyzed trends in abundance forC. leucas andA. spatula using generalized linear models with a negative binomial error structure and a log link. Lake Pontchartrain data were divided into four spatial locations (northwest, northeast, southwest, southeast) since each region represents a unique combination of anthropogenic and natural influences that could affect catches. For each species and gear type, we produced log-likelihood profiles for the instantaneous rate of change in relative abundance through time. Raw catches were generally lower for both species in the later surveys.C. leucas were not captured in beach seines since the 1950s andA. spatula were rarely captured in trawls or seines since the 1970s. Likelihood profiles of changes in abundance forC. leucas andA. spatula showed very large declines in both species since 1953.C. leucas declined by 98.6% (95% CI: 73.4–99.9%) in gillnets and became functionally extirpated in beach seines with a decline of 99.9% (95% CI: 23–99.9%). Among all gears,C. leucas declined by the same rate as in gillnets. The decline inA. spatula was also large with a decrease of 98.6% (95% CI: 73.4–99.9%) in beach seines and a decline of 99.2% (95% CI: 54.8–99.9%) in trawls since 1953. Catches ofA. spatula in gillnets did not show a significant change over the study period. The continued decline of these two apex predators could seriously affect efforts to restore this degraded estuarine ecosystem.     

A study of heavy metal pollution in the Tinto-Odiel estuary in southwestern Spain using factor analysis

The estuary of Odiel and Tinto rivers, located on the southwestern coast of the Iberian Peninsula, receives acidic fluvial water discharges with high concentrations of sulphates and heavy metals from these rivers. In addition, a big industrial complex which efflues directly on the system is located in the same estuary. The effluents induce the presence in the estuary of high concentrations of heavy metals and phospates (nutrients). The application of factorial analysis techniques on the nutrients and heavy metal concentrations in 46 water samples taken from 32 different sampling stations located along the estuary, allows three groups of elements and compounds with a distinct origin to be determinated. So, Cu and Zn have a clear fluvial provenance, whereas PO₄ and As are clearly industrial wastes and Cl, K, Ca, Li, Rb and Sr come from the sea. From the factorial analyses we can deduce the existence of two agents controlling the behavior of the analyzed elements, which are: the tidal exchange with the open sea and the fluvial supply. Received: 20 November 1998 · Accepted: 11 August 1999     

High‐Arctic climate conditions for the last 7000 years inferred from multi‐proxy analysis of the Bliss Lake record,North Greenland

The Arctic is more vulnerable to climate change than are mid latitudes. Therefore, palaeolimnological studies from the High Arctic are important in providing insights into the dynamics of the climate system. Here we present a multi‐proxy study from one of the world's northernmost lakes: Bliss Lake, Peary Land, Greenland. The early Holocene (10 850–10 480 cal. a BP) is characterized by increased erosion and gradually more marine conditions. Full marine conditions developed from 10 480 cal. a BP until the lake was isolated at 7220 cal. a BP. From its marine isolation at 7220 cal. a BP Bliss Lake becomes a lacustrine environment. Evidence from geochemical proxies (δ¹³C and total organic carbon) suggests that warmer conditions prevailed between 7220 and 6500 cal. a BP, corresponding to the Holocene thermal maximum, and from 3300 until 910 cal. a BP. From 850 to 500 cal. a BP colder climate conditions persisted. The transition from warmer to colder climate conditions taking place around 850 cal. a BP may be associated with the transition from the Medieval Warm Period to the Little Ice Age. Copyright © 2011 John Wiley & Sons, Ltd.     

Vegetation and climate changes over the last 30 000 years on the Leizhou Peninsula,southern China,inferred from the pollen record of Huguangyan Maar Lake

A pollen record from Huguangyan Maar Lake documents regional palaeovegetation and palaeoclimate changes in southern China over the last 30 000 years. Huguangyan Maar Lake is located close to the South China Sea (SCS) coastline and is influenced by the East Asian Monsoon (EAM). The pollen assemblages show a succession of vegetation and climate changes. During the Last Glaciation, 30–15.8 cal. ka BP, the Huguangyan area was dominated by subtropical evergreen‐deciduous forest with grassland surrounding the lake, indicating a colder and drier climate than today. During 15.8–11 cal. ka BP, the study area experienced several climatic fluctuations. From 11 to 2 cal. ka BP, the climate shifted to warmer and wetter conditions. After the Holocene Optimum in the early Holocene, the temperature and precipitation decreased. The sediment record of the last 2000 years cannot be used to interpret natural palaeoclimate changes due to the intense anthropogenic influences. Overall, however, the Huguangyan pollen archive highlights the rapid responses of subtropical vegetation to insolation changes in southern China.     

6600 years of earthquake record in the Julian Alps (Lake Bohinj,Slovenia)

Sequences of lake sediments often form long and continuous records that may be sensitive recorders of seismic shaking. A multi‐proxy analysis of Lake Bohinj sediments associated with a well‐constrained chronology was conducted to reconstruct Holocene seismic activity in the Julian Alps (Slovenia). A seismic reflection survey and sedimentological analyses identified 29 homogenite‐type deposits related to mass‐wasting deposits. The most recent homogenites can be linked to historical regional earthquakes (i.e. 1348 ad , 1511 ad and 1690 ad ) with strong epicentral intensity [greater than ‘damaging’ (VIII ) on the Medvedev–Sponheuer–Karnik scale]. The correlation between the historical earthquake data set and the homogenites identified in a core isolated from local stream inputs, allows interpretation of all similar deposits as earthquake related. This work extends the earthquake chronicle of the last 6600 years in this area with a total of 29 events recorded. The early Holocene sedimentary record is disturbed by a seismic event (6617 ± 94 cal yr bp ) that reworked previously deposited sediment and led to a thick sediment deposit identified in the seismic survey. The period between 3500 cal yr bp and 2000 cal yr bp is characterized by a major destabilization in the watershed by human activities that led to increases in erosion and sedimentation rates. This change increased the lake's sensitivity to recording an earthquake (earthquake‐sensitivity threshold index) with the occurrence of 72 turbidite‐type deposits over this period. The high turbidite frequency identified could be the consequence of this change in lake earthquake sensitivity and thus these turbidites could be triggered by earthquake shaking, as other origins are discarded. This study illustrates why it is not acceptable to propose a return period for seismic activity recorded in lake sediment if the sedimentation rate varies significantly.     

Chemical weathering over the last 1200 years recorded in the sediments of Gonghai Lake,Lvliang Mountains,North China: a high‐resolution proxy of past climate

Increasing interest in global climate change has led to attempts to understand and quantify the relationship between chemical weathering processes and environmental conditions, especially climate. This interest necessitates the identification of new climate proxies for the reconstruction of two important Earth surface processes: physical erosion and chemical weathering. In this study, an AMS ¹⁴C‐dated 2.8‐m‐long sediment core, GH09B1, from Lake Gonghai in north‐central China was subjected to detailed geochemical analyses to evaluate the intensity of chemical weathering conditions in the catchment. Multivariate statistical analysis of major and trace elemental data of 139 subsamples revealed that the first principal component axis PCA1 explained ～53% of the variance in the assemblage of elements/oxides with significant positive correlations between PCA1 scores and the separation of mobile and soluble elements/oxides from the immobile and resistant elements/oxides, which is thus able to indicate the chemical weathering in the catchment. These results are supported by the down‐core trends of other major and trace elemental ratios of chemical weathering intensity as well as by pollen data from the same core. Variations in PCA1, chemical index of alteration (CIA), Rb/Sr ratio and other oxides ratios indicate stronger chemical weathering due to a wet climate during the Medieval Warm Period (MWP). However, the MWP was interrupted by an interval of relatively weaker chemical weathering conditions from AD 940–1070. Weak chemical weathering under a dry climate occurred during the Little Ice Age (LIA), and increased chemical weathering intensity during the Current Warm Period (CWP). Our proxy records of chemical weathering over the last millennium correlate well with the available proxy records of precipitation from Gonghai Lake as well as with the speleothem oxygen isotope record from Wanxiang Cave, but do not show a significant correlation with the temperature record in N China, suggesting that the chemical weathering intensity in the study area was mainly controlled by the amount of rainfall rather than by temperature. We conclude that high resolution lacustrine sediment geochemical parameters can be used as reliable proxies for climate variations at centennial‐decadal time scales.     

Climatic and environmental changes in the Yana Highlands of north-eastern Siberia over the last c. 57 000 years,derived from a sediment core from Lake Emanda

The sediment succession of Lake Emanda in the Yana Highlands was investigated to reconstruct the regional late Quaternary climate and environmental history. Hydro-acoustic data obtained during a field campaign in 2017 show laminated sediments in the north-western and deepest (up to ̃15 m) part of the lake, where a ̃6-m-long sediment core (Co1412) was retrieved. The sediment core was studied with a multi-proxy approach including sedimentological and geochemical analyses. The chronology of Co1412 is based on ¹⁴C AMS dating on plant fragments from the upper 4.65 m and by extrapolation suggests a basal age of c. 57 cal. ka BP. Pronounced changes in the proxy data indicate that early Marine Isotope Stage (MIS) 3 was characterized by unstable environmental conditions associated with short-term temperature and/or precipitation variations. This interval was followed by progressively colder and likely drier conditions during mid-MIS 3. A lake-level decline between 32.0 and 19.1 cal. ka BP was presumably related to increased continentality and dry conditions peaking during the Last Glacial Maximum (LGM). A subsequent rise in lake level could accordingly have been the result of increased rainfall, probably in combination with seasonally high meltwater input. A milder or wetter Lateglacial climate increased lake productivity and vegetation growth, the latter stabilizing the catchment and reducing clastic input into the lake. The Bølling-Allerød warming, Younger Dryas cooling and Holocene Thermal Maximum (HTM) are indicated by distinct changes in the environment around Lake Emanda. Unstable, but similar-to-present-day climatic and environmental conditions have persisted since c. 5 cal. ka BP. The results emphasize the highly continental setting of the study site and therefore suggest that the climate at Lake Emanda was predominantly controlled by changes in summer insolation, global sea level, and the extent of ice sheets over Eurasia, which influenced atmospheric circulation patterns.     

Temporal changes in the phytoplankton community of the southern basin of Lake Baikal over the last 24,000 years recorded by photosynthetic pigments in a sediment core

Photosynthetic pigments and other indicators of phytoplankton were analyzed in a dated undisturbed sediment core obtained from the southern basin of Lake Baikal to reveal temporal changes in the phytoplankton community in the lake through the last glacial/post-glacial transition. The sedimentation age of the core spans the last 24 ¹⁴C ka. Chlorophyll a, its derivatives, carotenoids and total organic carbon (TOC) started to increase after 15 ¹⁴C ka, and the onset of biogenic silica occurred at 10 ¹⁴C ka. This indicated that the post-glacial growth of diatoms was preceded by that of other phytoplankton groups. In the record of the pigments and TOC, a temporary decrease was observed in the period 11.5–10.5 ¹⁴C ka, corresponding to the Younger Dryas cold period. The similarity found between the depth profiles of pyropheophytin a and steryl chlorin esters formed through predation of phytoplankton by zooplankton and that of TOC suggested the important contribution of fecal pellets to sedimentary organic matter in the lake.     

Face stability analysis of shallow shield tunnels in dry sandy ground using the discrete element method

Controlling the face stability of shallow shield tunnels is difficult due to the inadequate understanding of face failure mechanism. The failure mechanism and the limit support pressure of a tunnel face in dry sandy ground were investigated by using discrete element method (DEM), which has particular advantages for revealing mechanical properties of granular materials. The contact parameters of the dry sand particles were obtained by calibrating the results of laboratory direct shear tests. A series of three-dimensional DEM models for different ratios of the cover depth to the diameter of the tunnel (C/D = 0.5, 1, and 2; i.e., relative depth) were then built to simulated the process of tunnel face failure. The limit support pressure, failure zone and soil arching were discussed and compared with other methods. The results of DEM simulations show that the process of tunnel face failure can be divided into two stages. With the increase of the horizontal displacement of the tunnel face, the support pressure decreases to the limit support pressure and then increases to the residual support pressure. The limit support pressure increases with the rise of relative depth and then tends to be constant. In the process of tunnel face failure, the failure zone is gradually enlarged in size and expands to the ground surface. The numerical results also demonstrate that soil arching occurs in the upper part of the failure zone and the soil becomes loosened in the failure zone. Consequently, the comprehensive analysis of tunnel face failure may help to guarantee safe construction during tunneling.     

Diatom‐based reconstruction of summer sea‐surface salinity in the South China Sea over the last 15 000 years

We present a new reconstruction of summer sea‐surface salinity (SSS) over the past 15 000 years based on a diatom record from piston core 17940, located on the northern slope of the South China Sea (SCS). The reconstructed diatom‐based summer SSS values for the modern period are in accord with instrumental observations of summer SSS in the area. Here, the modern summer SSS is primarily controlled by river runoff, in particular from the Pearl River. The reconstruction presented in this study shows that the summer SSS varied between 33.3 and 34.2 psu over the past 15 000 years. The long‐term summer SSS trend closely followed the trend of the orbitally controlled solar insolation at 20°N, suggesting that orbital forcing was the dominant driver of changes in summer SSS in this area. Comparisons to speleothem δ¹⁸O data and studies of surface hydrography in the region suggest that changes in solar insolation affected the summer SSS through changes in the East Asian Monsoon and sea‐level changes associated with the last deglaciation. Univariate spectral analyses indicate that centennial‐scale oscillatory variations in summer SSS were superimposed on the long‐term trend. During the deglacial period (c. 12 000–9000 cal. a BP), the dominant periodicity was centred around 230–250 years, whereas a ～350‐year oscillation dominated in the period 2200–4500 cal. a BP. The balance of evidence suggests that these centennial‐scale changes in summer SSS may have been driven by solar‐induced changes in the East Asian Monsoon, but further evidence is needed to firmly establish this relationship.