The Atlantic meridional overturning circulation (AMOC) is a system of ocean currents that has an essential role in Earth's climate, redistributing heat and influencing the carbon cycle. The AMOC has been shown to be weakening in recent years ; this decline may reflect decadal-scale variability in convection in the Labrador Sea, but short observational datasets preclude a longer-term perspective on the modern state and variability of Labrador Sea convection and the AMOC. Here we provide several lines of palaeo-oceanographic evidence that Labrador Sea deep convection and the AMOC have been anomalously weak over the past 150 years or so (since the end of the Little Ice Age, LIA, approximately AD 1850) compared with the preceding 1,500 years. Our palaeoclimate reconstructions indicate that the transition occurred either as a predominantly abrupt shift towards the end of the LIA, or as a more gradual, continued decline over the past 150 years; this ambiguity probably arises from non-AMOC influences on the various proxies or from the different sensitivities of these proxies to individual components of the AMOC. We suggest that enhanced freshwater fluxes from the Arctic and Nordic seas towards the end of the LIA-sourced from melting glaciers and thickened sea ice that developed earlier in the LIA-weakened Labrador Sea convection and the AMOC. The lack of a subsequent recovery may have resulted from hysteresis or from twentieth-century melting of the Greenland Ice Sheet . Our results suggest that recent decadal variability in Labrador Sea convection and the AMOC has occurred during an atypical, weak background state. Future work should aim to constrain the roles of internal climate variability and early anthropogenic forcing in the AMOC weakening described here.

1. Submerged macrophyte and phytoplankton components of eutrophic, shallow lakes have frequently undergone dynamic changes in composition and abundance with important consequences for lake functioning and stability. However, because of a paucity of long-term survey data, we know little regarding the nature, direction and sequencing of such changes over decadal-centennial or longer timescales. 2. To circumvent this problem, we analysed multiple (n = 5) chronologically correlated sediment cores for plant macro-remains and a single core for pollen and diatoms from one small, shallow, English lake (Felbrigg Hall Lake, Norfolk, U.K.), documenting 250 years of change to macrophyte and algal communities. 3. All five cores showed broadly similar stratigraphic changes in macrophyte remains with three distinct phases of macrophyte development: Myriophyllum-Chara-Potamogeton (c. pre-1900), to Ceratophyllum-Chara- Potamogeton (c. 1900Potamogeton (c. -1960 and finally to Zannichellia-Potamogeton (c. post-1960). Macrophyte species richness declined from at least 10 species pre-1900 to just four species at the present day. Additionally, in the final Zannichellia-Potamogeton phase, a directional shift between epi-benthic and phytoplanktonbased primary production was indicated by the diatom data. 4. Based on macrophyte-seasonality relationships established for the region, concomitant with the final shift to Zannichellia-Potamogeton, we infer a reduction in the seasonal duration of plant dominance (plant-covered period). Furthermore, we hypothesise that this change in species composition resulted in a situation whereby macrophyte populations were seasonally 'sandwiched' between two phytoplankton peaks in spring and late summer as observed in the contemporary lake. 5. We suggest that eutrophication-induced reductions in macrophyte species richness, especially if the number of plant-seasonal strategies is reduced, may constrict the plant growing season. In turn, this may render a shallow lake increasingly vulnerable to seasonal invasions of phytoplankton resulting in further species losses in the plant community. Thus, as part of a slow (over perhaps 10-100s of years) and self-perpetuating process, macrophytes may be gradually pushed out by phytoplankton without the need for a perturbation as required in the alternative stable states model of plant loss.

Summary1. Priority question exercises are becoming an increasingly common tool to frame future agendas in conservation and ecological science. They are an effective way to identify research foci that advance the field and that also have high policy and conservation relevance. 2. To date, there has been no coherent synthesis of key questions and priority research areas for palaeoecology, which combines biological, geochemical and molecular techniques in order to reconstruct past ecological and environmental systems on time-scales from decades to millions of years. 3. We adapted a well-established methodology to identify 50 priority research questions in palaeoecology. Using a set of criteria designed to identify realistic and achievable research goals, we selected questions from a pool submitted by the international palaeoecology research community and relevant policy practitioners. 4. The integration of online participation, both before and during the workshop, increased international engagement in question selection. 5. The questions selected are structured around six themes: human-environment interactions in the Anthropocene; biodiversity, conservation and novel ecosystems; biodiversity over long time-scales; ecosystem processes and biogeochemical cycling; comparing, combining and synthesizing information from multiple records; and new developments in palaeoecology. 6. Future opportunities in palaeoecology are related to improved incorporation of uncertainty into reconstructions, an enhanced understanding of ecological and evolutionary dynamics and processes and the continued application of long-term data for better-informed landscape management. 256-26750 priority research questions in palaeoecology 257 7. Synthesis. Palaeoecology is a vibrant and thriving discipline, and these 50 priority questions highlight its potential for addressing both pure (e.g. ecological and evolutionary, methodological) and applied (e.g. environmental and conservation) issues related to ecological science and global change.

Concentrations are reported of hexabromocyclododecanes (HBCDs) and tetrabromobisphenol-A (TBBP-A) in water (n = 27), sediment (n = 9), and fish samples (n = 30) from nine English lakes. Seasonal variation in concentrations in water is minimal. Concentrations of TBBP-A range from 140 to 3200 pg L(-1) (water), 330 to 3800 pg g(-1) dry weight (sediment), and <0.29 to 1.7 ng g(-1) lipid weight (fish). Those of SigmaHBCDs range between 80 and 270 pg L(-1) (water), 880 and 4800 pg g(-1) dry weight (sediment), and 14 and 290 ng g(-1) lipid weight (fish). Aqueous concentrations of SigmaHBCDs and TBBP-A are significantly positively correlated, indicating a common source. Average +/-sigma(n) "freely-dissolved" phase proportions are 47 +/- 4.7% (SigmaHBCDs) and 61 +/- 2.9% (TBBP-A). Average field-derived bioaccumulation factors are 5900, 1300, 810, and 2100 for alpha-, beta-, gamma-, and SigmaHBCDs, respectively. Tetrabromocyclododecadienes are detected in all sediments, with pentabromocyclododecenes present in some. This suggests HBCD degrades via sequential loss of HBr. The delta-HBCD meso form was quantified in 43% of fish samples (1.0-11% SigmaHBCDs). Its absence from temporally and spatially consistent water and sediment samples suggests it is formed via bioisomerization. While HBCD chiral signatures are racemic in water and sediment, our data reveal enantiomeric enrichment of (-)alpha-HBCD and (+)gamma-HBCD in fish.

The Anthropocene as a potential new unit of the International Chronostratigraphic Chart (which serves as the basis of the Geological Time Scale) is assessed in terms of the stratigraphic markers and approximate boundary levels available to define the base of the unit. The task of assessing and selecting potential Global Boundary Stratotype Section and Point (GSSP) candidate sections, a required part of the process in seeking formalisation of the term, is now being actively pursued. Here, we review the suitability of different stratified palaeoenvironmental settings and facies as potential hosts for a candidate GSSP and auxiliary sections, and the relevant stratigraphical markers for correlation. Published examples are evaluated for their strengths and weaknesses in this respect. A marked upturn in abundance of radioisotopes of 239 Pu or 14 C, approximately in 1952 and 1954 CE respectively, broadly coincident with a downturn in δ 13 C values, is applicable across most environments. Principal palaeoenvironments examined include: settings associated with accumulations of anthropogenic material, marine anoxic basins, coral reefs, estuaries and deltas, lakes at various latitudes, peat bogs, snow/ice layers, speleothems and trees.Together, many of these geographically diverse palaeoenvironments offer annual/subannual laminae that can be counted and independently dated radiometrically (e.g. by 210 Pb).Examples of possible sections offer the possibility of correlation with annual/seasonal resolution. From among such examples, a small number of potentially representative sites require the acquisition of more systematic and comprehensive datasets, with correlation established between sections, to allow selection of a candidate GSSP and auxiliary stratotypes. The assessments in this paper will help find the optimal locations for these sections.

Growth in fundamental drivers—energy use, economic productivity and population—can provide quantitative indications of the proposed boundary between the Holocene Epoch and the Anthropocene. Human energy expenditure in the Anthropocene, ~22 zetajoules (ZJ), exceeds that across the prior 11,700 years of the Holocene (~14.6 ZJ), largely through combustion of fossil fuels. The global warming effect during the Anthropocene is more than an order of magnitude greater still. Global human population, their productivity and energy consumption, and most changes impacting the global environment, are highly correlated. This extraordinary outburst of consumption and productivity demonstrates how the Earth System has departed from its Holocene state since ~1950 CE, forcing abrupt physical, chemical and biological changes to the Earth’s stratigraphic record that can be used to justify the proposal for naming a new epoch—the Anthropocene.

1. Sedimentary remains of aquatic plants, both vegetative (turions, leaves, spines) and reproductive (fruits, seeds, pollen), may provide a record of temporal changes in the submerged vegetation of lakes. An independent assessment of the degree to which these remains reflect past floristic change is, however, rarely possible. 2. By exploiting an extensive series of historical plant records for a small shallow lake we compare plant macrofossil (three cores) and pollen (one core) profiles with the documented sequence of submerged vegetation change since c. 1750 AD. The data set is based on 146 site visits with 658 observations including 42 taxa classified as aquatic, spanning 250 years.3. Approximately 40% of the historically recorded aquatic taxa were represented by macro-remains. In general macrofossils underestimated past species diversity, with pondweeds (three of eight historically recorded Potamogeton species were found) particularly poorly represented. Nonetheless, several taxa not reported from historical surveys (e.g. Myriophyllum alterniflorum and Characeae) were present in the sediment record. 4. The pollen record revealed taxa which left no macro-remains (e.g. Littorella uniflora), and the macrofossil record provided improved taxonomic resolution for some taxa (e.g. Potamogeton) and a more reliable record of persistence, appearance and loss of others (e.g. Myriophyllum spp. and Nymphaeaceae). 5. Detrended correspondence analysis indicated that changes in the community composition evidenced by the palaeolimnological and historical records were synchronous and of a similar magnitude. Both records pointed to a major change at around 1800, with the historical record suggesting a more abrupt change than the sedimentary data. There was good agreement on a subsequent change c. 1930. 6. The palaeolimnological data did not provide a complete inventory of historically recorded species. Nevertheless, these results suggest that combined macrofossil and pollen records provide a reliable indication of temporal change in the dominant components of the submerged and floating-leaved aquatic vegetation of shallow lakes. As such palaeolimnology may provide a useful tool for establishing community dynamics and successions of plants over decadal to centennial timescales.

The diatom £ora of the lake is currently dominated by several species, such as Aulacoseira baicalensis, A. islandica, Cyclotella minuta and Stephanodiscus binderanus v. baicalensis. All these species, except for C. minuta, have become more common in the lake in approximately the last 130 years, and we hypothesize that these changes may be attributed to a number of di¡erent processes linked to an ameliorating climate after the end of the Little Ice Age. The results presented here have important implications for this recently designated World Heritage Site, with regard to future pollution controls and catchment management policies.