The shellfish enigma across the Mesolithic-Neolithic transition in southern Scandinavia

The well-known and widespread replacement of oysters (abundant during the Mesolithic period) by cockles and mussels in many Danish Stone Age shell middens ca. 5900 cal yrs BP coincides with the transition to agriculture in southern Scandinavia. This human resource shift is commonly believed to reflect changing resource availability, driven by environmental and/or climatic change at the Mesolithic-Neolithic transition rather than cultural choice. While several hypotheses have been proposed to explain the “Mesolithic-Neolithic oyster decline”, an explanation based on a sudden freshening of the inner Danish waters has received most attention. Here, for the first time, we test and refute this long-standing hypothesis that declining salinity explains the marked reduction in oysters identified within numerous shell middens across coastal Denmark at the Mesolithic-Neolithic transition using quantitative and qualitative salinity inference from several, independent proxies (diatoms, molluscs and foraminifera) from multiple Danish fjord sites. Alternatively, we attribute the oyster decline to other environmental causes (particularly changing sedimentation), ultimately driven by external climatic forcing. Critical application of such high-quality environmental archives can reinvigorate archaeological debates and can aid in understanding and managing environmental change in increasingly impacted coastal regions

The effect of rhEpo on V̇O₂max depends on the O₂ inspiration fraction.

<p>This figure refers to the non-invasive study. Panel A shows the individual V̇O₂max values measured before (−) and after (+) a 5-week treatment with recombinant human erythropoieitin (rhEpo), during normoxia and acute hypoxia equivalent to altitudes ranging between 1500 m and 4500 m. Panel B indicates the changes in V̇O₂max induced by rhEpo, for each altitude condition. Values are means±SE in seven subjects. *P<0.05 after <i>vs</i> before rhEpo. ‡P<0.05 hypoxia (3500 m) <i>vs</i> normoxia (0 m).</p

Agreement between impedance and dye dilution for cardiac output measurement.

<p>This graph shows the agreement (Bland-Altman plot) between the cardiac impedance technique and the indocyanine-green dye dilution method for measuring cardiac output during exercise obtained from 55 measurements in seven subjects. For each measurement, the difference between the two methods is plotted against the average of both techniques. The solid line indicates the mean bias, while the dotted lines indicate the 95% confidence intervals (2×standard deviation).</p

Following rhEpo, blood flow redistribution occurs in normoxia but not in severe acute hypoxia.

<p>This figure refers to the invasive study. Two-leg blood flow over cardiac output is plotted against power output in the four experimental conditions, i.e. before and after a 14-week treatment with recombinant human erythropoieitin (rhEpo) during normoxia and acute hypoxia equivalent to an altitude of 4500 m. Values are means±SE in seven subjects. *P<0.05 after <i>vs</i> before rhEpo. §P<0.05 hypoxia <i>vs</i> normoxia.</p

rhEpo increases peak pulmonary and leg V̇O₂ in normoxia but not in severe acute hypoxia.

<p>This figure refers to the invasive study. Pulmonary V̇O₂ (panel A) and leg V̇O₂ (panel B) are plotted against power output in the four experimental conditions, i.e. before and after a 14-week treatment with recombinant human erythropoieitin (rhEpo) during normoxia and acute hypoxia equivalent to an altitude of 4500 m. Values are means±SE in seven subjects. *P<0.05 after <i>vs</i> before rhEpo. §P<0.05 hypoxia <i>vs</i> normoxia.</p

Systemic and leg O₂ transport variables after rhEpo in normoxia and in severe acute hypoxia.

<p>This figure refers to the invasive study. Cardiac output (panel A), systemic O₂ delivery (panel B), systemic arterio-venous O₂ difference (Syst. A-v O₂ diff.) (panel C), systemic O₂ extraction (panel D), leg blood flow (panel E), leg O₂ delivery (panel F), leg arterio-venous O₂ difference (Leg a-v0₂ diff) (panel G) and leg O₂ extraction (panel H) are plotted against power output in the four experimental conditions, i.e. before and after a 14-week treatment with recombinant human erythropoieitin (rhEpo) during normoxia and acute hypoxia equivalent to an altitude of 4500 m. Values are means±SE in seven subjects. *P<0.05 after <i>vs</i> before rhEpo. §P<0.05 hypoxia <i>vs</i> normoxia.</p

Acid-base balance, lactate, respiratory exchange ratio and ventilation during the invasive experiment.

<p>Values are means±SE (n = 7). a, arterial; fv, femoral vein; V̇_E/V̇O₂ and V̇_E/V̇CO₂, ventilatory equivalents for O₂ and CO₂, respectively. RER, respiratory exchange ratio. The subjects were evaluated before (PRE) and after a 14-week treatment with recombinant human Epo (POST), each time in normoxia and in acute normobaric hypoxia equivalent to 4500 m of altitude. ^*P<0.05 POST <i>vs</i> PRE. ^§P<0.05 hypoxia <i>vs</i> normoxia.</p

Nutrients and saltwater exchange as drivers of environmental change in a Danish brackish coastal lake over the past 100 years

Many northwest European lake systems are suffering from the effects of eutrophication due to continued loading and/or poor, ineffective management strategies. Coastal brackish lakes are particularly difficult to manage due to complex nitrogen, phosphorus, and salinity dynamics that may exert varying influence on lake biological communities, but long-term data on how these important and often biodiverse systems respond to change are rare. In this study, palaeolimnological data (including sedimentary parameters, diatoms, and plant macrofossils) and environmental monitoring data (for the last ~40 years) have been used to assess environmental change over the last 100 years in Kilen, a brackish lake in northwest Jutland, Denmark. Kilen has been regularly monitored for salinity (since 1972), TP (from 1975), TN (from 1976), and since 1989 for biological data (phytoplankton, zooplankton, and macrophytes), which allows a robust comparison of contemporary and paleolimnological data at high temporal resolution. The palaeolimnological data indicate that the lake has been nutrient rich for the last 100 years, with eutrophication peaking from the mid-1980s to the late 1990s. Reduced nutrient concentrations have occurred since the late 1990s, though this is not reflected in the sediment core diatom assemblage, highlighting that caution must be taken when using quantitative data from biological transfer functions in paleolimnology. Lake recovery over the last 20 years has been driven by a reduction in TN and TP loading from the catchment and shows improvements in the lake water clarity and, recently, in macrophyte cover. Reduced salinity after 2004 has also changed the composition of the dominant macrophyte community within the lake. The low N:P ratio indicates that in summer, the lake is predominately N-limited, likely explaining why previous management, mainly focusing on TP reduction measures, had a modest effect on the water quality of the lake. Despite a slight recovery, the lake is still nutrient-rich, and future management of this system must continue to reduce the nutrient loads of both TN and TP to ensure sustained recovery. This study provides an exceptional opportunity to validate the palaeolimnological record with monitoring data and demonstrates the power of using this combined approach in understanding environmental change in these key aquatic ecosystems

Experimental protocol.

<p>Summary of the experimental design, which involved two separate experiments in the same group of subjects: 1) a non-invasive study, and 2) an invasive study. The data on red blood cell volume (RCV) are available in a separate report <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002996#pone.0002996-Lundby1" target="_blank">[6]</a>.</p

Maximal exercise variables during the non-invasive experiment.

<p>Values are means±SE (n = 7). ^a reflects arterialized samples from capillary blood; ^v reflects arm venous samples. RER, respiratory exchange ratio. The subjects were evaluated before (PRE) and after a 5-week treatment with recombinant human Epo (POST), in normoxia and in acute normobaric hypoxia equivalent to altitudes ranging from 1500 m to 4500 m. ^*P<0.05 POST <i>vs</i> PRE. ^§P<0.05 hypoxia <i>vs</i> normoxia.</p