ALBERT

Description: The creation of networks of shell-based chronologies which can provide regionally extensive high-resolution proxies for the marine environment depends on the spatial extent of the common environmental signal preserved in the shell banding and on the reliability of the dating model. Here Arctica islandica chronologies from five neighboring sites in the North Sea are compared, and the strength of the common environmental signal across distances up to 80 km is analyzed using statistical techniques derived from dendrochronology. The signal is found to be coherent across these distances. In a linked study, chronologies based on one of the same sites but constructed by two different research teams are compared. Methodological differences in increment interpretation are found to lead to slippage in the dating models. Systematic inclusion or exclusion of intermittently occurring increments results in the two chronologies becoming misaligned by 4 years over a 70-year period. Comparisons with neighboring chronologies indicate that such increments can generally be regarded as genuine annual increments even if they are not visible in all shells.

Description: The identification in various proxy records of periods of rapid (decadal scale) climate change over recent millennia, together with the possibility that feedback mechanisms may amplify climate system responses to increasing atmospheric CO2, highlights the importance of a detailed understanding, at high spatial and temporal resolutions, of forcings and feedbacks within the system. Such an understanding has hitherto been limited because the temperate marine environment has lacked an absolute timescale of the kind provided by tree-rings for the terrestrial environment and by corals for the tropical marine environment. Here we present the first annually resolved, multi-centennial (489-year), absolutely dated, shell-based marine master chronology. The chronology has been constructed by detrending and averaging annual growth increment widths in the shells of multiple specimens of the very long-lived bivalve mollusc Arctica islandica, collected from sites to the south and west of the Isle of Man in the Irish Sea. The strength of the common environmental signal expressed in the chronology is fully comparable with equivalent statistics for tree-ring chronologies. Analysis of the 14C signal in the shells shows no trend in the marine radiocarbon reservoir correction (DR), although it may be more variable before ~1750. The d13C signal shows a very significant (R**2 = 0.456, p 〈 0.0001) trend due to the 13C Suess effect.

Description: We demonstrate here that the growth increment variability in the shell of the long-lived bivalve mollusc Arctica islandica can be interpreted as an indicator of marine environmental change in the climatically important North Atlantic shelf seas. Multi-centennial (up to 489-year) chronologies were constructed using five detrending techniques and their characteristics compared. The strength of the common environmental signal expressed in the chronologies was found to be fully comparable with equivalent statistics for tree-ring chronologies. The negative exponential function using truncated increment-width series from which the first thirty years have been removed was chosen as the optimal detrending technique. Chronology indices were compared with the Central England Temperature record and with seawater temperature records from stations close to the study site in the Irish Sea. Statistically significant correlations were found between the chronology indices and (a) mean air temperature for the 14-month period beginning in the January preceding the year of growth, (b) mean seawater temperatures for February-October in the year preceding the year of growth (c) late summer and autumn air temperatures and sea surface temperatures for the year of growth and (d) the timing of the autumn decline in SST. Changes through time in the correlations with air and seawater temperatures and changes towards a deeper water origin for the shells in the chronology were interpreted as an indication that shell growth may respond to stratification dynamics.

Description: A multicentennial and absolutely-dated shell-based chronology for the marine environment of the North Icelandic Shelf has been constructed using annual growth increments in the shell of the long-lived bivalve clam Arctica islandica. The region from which the shells were collected is close to the North Atlantic Polar Front and is highly sensitive to the varying influences of Atlantic and Arctic water masses. A strong common environmental signal is apparent in the increment widths, and although the correlations between the growth increment indices and regional sea surface temperatures are significant at the 95% confidence level, they are low (r ~ 0.2), indicating that a more complex combination of environmental forcings is driving growth. Remarkable longevities of individual animals are apparent in the increment-width series used in the chronology, with several animals having lifetimes in excess of 300 years and one, at 507 years, being the longest-lived non-colonial animal so far reported whose age at death can be accurately determined. The sample depth is at least three shells after AD 1175, and the time series has been extended back to AD 649 with a sample depth of one or two by the addition of two further series, thus providing a 1357-year archive of dated shell material. The statistical and spectral characteristics of the chronology are investigated by using two different methods of removing the age-related trend in shell growth. Comparison with other proxy archives from the same region reveals several similarities in variability on multidecadal timescales, particularly during the period surrounding the transition from the Medieval Climate Anomaly to the Little Ice Age.

Description: This dataset contains salinity and stable isotope measurements taken of water samples collected during an October 2016 research cruise in the Gulf of Maine aboard the NOAA ship Pisces. Water samples were collected at 44 different stations throughout the Gulf of Maine at various depths from the surface to the seafloor using a carousel sampler with 12 different Niskin bottles and attached to a SeaBIRD 911 CTD. Salinity was measured in situ using the SeaBird 911 CTD with auxiliary sensors. Water samples were collected from depth in Niskin bottles and transferred to triple rinsed Thermo Scientific Nalgene 4 Oz natural hdpe plastic wide mouth leakproof bottles. Parafilm was secured around the cap of each bottle to help prevent evaporation. Samples designated for δ18O(water) analyses were stored in containers in the wet lab of the boat. Samples designated for δ15N(NO3-) and δ18O(NO3-) analyses were immediately placed in a walk-in freezer set at − 8°C. Once back at port, samples were overnight shipped to the Stable Isotope Lab at Iowa State University. Frozen samples were shipped in coolers with additional ice added and, upon arrival, immediately placed back in a freezer. This dataset also contains two freshwater samples collected from the Kennebec River in November and December 2016. Samples were hand collected and stored in Thermo Scientific Nalgene 4 Oz natural hdpe plastic wide mouth leakproof bottles. Samples were shipped on dry ice to Iowa State University and processed in the same way as the other saltwater samples as detailed below. Once at Iowa State University, samples designated for δ18O(water) were stored in the temperature controlled laboratory and then analyzed using a Picarro L2130-I Isotopic Liquid Water Analyzer with attached autosampler. Three different isotopic reference standards, VSMOW, USGS 48, and USGS 47, were used. At least one reference standard sample was used per 5 samples. The average combined uncertainty (analytical and average correction factor) was ±0.20‰ (2σ). Samples designated for isotopic analyses (δ15N and δ18O) of dissolved NO3- were first unfrozen at Iowa State University and filtered using 0.2 μm pore filters (Sartorius Minisart high flow syringe sterile PES membrane). Subsequently, water samples were treated with sulfamic acid (ACS grade, 99.3-100.3%) to remove any NO2- following the procedures outlined in Granger and Sigman (2009; doi:10.1002/rcm.4307). Briefly, glassware was acid washed and baked at 500°C. 60 ml of sample were treated with 600 μL 0.4M sulfamic acid (made using 10% v/v HCl) to reduce the pH to between 1.6 and 1.8, which is necessary to reduce NO2- to N2 and therefore remove it from the sample. After the reaction was allowed to occur for at least 5 min, samples were neutralized by adding 2M NaOH to the sample to return the sample to a pH of 7 (±0.5). Approximately 310 μL of NaOH were added to each sample but the exact amount of NaOH varied by sample and was determined using a pH meter. Samples were then refrozen, put on dry ice and shipped overnight to the University of California Davis Stable Isotope Facility. Samples were analyzed for δ15N(NO3-) and δ18O(NO3-) using the bacterial denitrification assay method as outlined by Sigman et al., (2001; doi:10.1021/ac010088e) and Casciotti et al., (2002; doi:10.1021/ac020113w), respectively. Isotopes were measured using a Thermoscientific Delta V Plus isotope ratio mass spectrometer coupled to a ThermoFinnigan GasBench + PreCon trace gas concentration system. Seven different reference standards were used to correct samples and report values on the international scale, Air: USGS34 KNO3, USGS35 NaNO3, Acros KNO3, Fisher KNO3, Strem KNO3, New Acros KNO3, and IAEA-NO-3 KNO3 (not used on all samples). Average analytical uncertainty (2σ) was ±0.5‰ for δ15N(NO3-) and ±0.3‰ for δ18O(NO3-). In order to assess the extent to which nitrification is occurring in the Gulf of Maine, we used the following equation for Δ(15, 18), first proposed by Sigman et al., (2005; doi:10.1029/2005GB002458): Δ(15, 18) = (δ15N(NO3-) - δ15Nm)-(15ε/18ε)x(δ18O(NO3-)-δ18Om) δ15Nm and δ18Om are mean δ15N and δ18O of dissolved NO3- in deep source waters, respectively. In this case, we use average values for samples taken at and below 100 m, where δ15N(NO3-) and δ18O(NO3-) remain relatively constant with depth. 15ε/18ε is the ratio of isotope fractionation factors for nitrogen and oxygen, respectively, for assimilation, which is taken to be 1 here. The propagated ([a2+b2]1/2) uncertainty for Δ(15, 18), calculated using the uncertainty associated with δ15N(NO3-) and δ18O(NO3-), is ±0.6‰ (2σ).

Description: These data include salinity and oxygen isotope measurements of water samples collected from coastal sites along the Gulf of Maine between 2003 and 2015. In particular, a suite of samples were collected along the coast of Maine, east of Penobscot Bay, on a monthly basis between April 2014 and March 2015. These data also include several freshwater samples collected from the Kennebec and Penobscot Rivers on a semi-monthly basis in 2014 and 2015. For the water samples with sample IDs starting with DSW, JSW, NSW, or OSW: The water samples were collected by hand from shore or boat using French square glass bottles with phenolic polycone lined caps. Salinity was measured using a Oakton SALT 6+ handheld salinity meter. Oxygen isotopes were measured using a Picarro L2130-i Isotopic Liquid Water Analyzer with an attached autosampler. Water samples with sample IDs starting with ASW were collected from shore. Samples with sample IDs starting with DMC 2010 were collected at the flowing seawater laboratory at the Darling Marine Center. Samples with sample IDs starting with Summer 2011 were collected from a boat. For these last 3 sample types (ASW, DMC 2010, Summer 2011): Salinity was measured with YSI Professional Plus salinity meter and oxygen isotopes were measured using a Picarro L1102-i Isotopic Liquid Water Analyzer with an attached autosampler. Data from Owen et al., 2008 and Wanamaker et al. (2006, 2007) was collected from the flowing seawater laboratory at the Darling marine center. Salinity was measured using a YSI model 85 oxygen, conductivity, salinity, and temperature system and oxygen isotopes were measured using a dual-inlet VG/Micromass SIRA (CO2–H2O equilibration method at 30 °C for 12 h).