POLNOR

R3 - Recent and subfossil biomineral skeletons of Arctic carbonate sediments and organisms as (paleo)environmental archives: a critical assessment

Following agreement of the collaborating partners of WP3 (IP PAS, IO PAN, and APN), during duration of the project (2014-2017) our teams were developing three main research themes (or perspectives) that included all tasks of the project: (1) Long-term paleontological perspective [based on Mesozoic/Cenozoic samples: IP PAS; Tasks T3.3, T3.4, T3.7]; (2) Short-term perspective: time scale of thousands/hundreds/tens of years [based on recent/sub-fossil samples: IO PAN, APN and IP PAS; Tasks T3.1, T3.3, T3.4, T3.5, T3.6, T3.8]; (3) Experimental perspective: time scale of months/days/hours [based on aquaria experiments: IP PAS, IO PAN, and APN; Tasks T 3.2, T3.3, T3.4, T3.8].

Theme #1: T3.3, T3.4, T3.7: IP PAS scientific team completed work on critical assessment of fossil, aragonitic samples (using corals as an example, but these are universal criteria that apply to all types of aragonite skeletal materials) as (paleo)environmental proxies. We have established the following criteria that confirm good preservation of the skeleton (in this particular case applied to corals, but the criteria are universal for all originally aragonitic fossils): (1) visual inspection of hand samples must indicate good preservation of skeletal morphology, (2) X-ray diffractometer (XRD) must indicate specimens are preserved as aragonite (except in cases where skeletons are infilled with cement), (3) optical microscopy and Scanning Electron Microscope (SEM) must show preservation of crystal ultrastructure, (4) Raman spectroscopy must suggest the absence of calcite within the skeleton, (5) results of SIMS and CL studies must indicate low Mn concentrations within the skeleton (but some groups of organisms, like mollusks, may naturally incorporate Mn into the skeleton), (6) trace element patterns found in most fossil samples must agree with those observed in most modern skeletons, (7) carbonate clumped isotope temperatures must be below 40°C, and (8) stratigraphic age inferred from the 87Sr/86Sr ratio must agree with independently determined stratigraphic age. The above criteria were first applied to test rigorously the preservation of the samples used to reconstruct geochemical conditions of the global ocean during Mesozoic and Cenozoic. In agreement with independent records, seawater Mg/Ca molar ratios inferred from the used proxies were low (Mg/Ca ~ 1) during the Cretaceous and Jurassic, and increased between the Early Cenozoic and present (Mg/Ca = 5.2) (see publications section D). Noteworthy, since diagenetic alteration of biogenic calcium carbonate samples may start instantly after animal's dead, the criteria 1, 2, 3 and if necessary also 4, were useful also to assess preservation quality of skeletal samples of modern Arctic organisms. Unexpectedly, despite of major geochemical fluctuations (including the transition from greenhouse conditions (Eocene) to icehouse conditions (Oligocene) and from low Mg/Ca "calcitic seas" during the Eocene through rapidly increasing Mg/Ca "aragonite seas" since the Oligocene), the well preserved skeletons of corals show a remarkable evolutionary stability of microstructural features, suggesting also stability of the biomineralization process which is controlled by organic macromolecules (see publications section D). This suggests that modifications of seawater geochemistry that occurred over millions of years, were probably accommodated by acclimating (evolving) organisms. This evolutionary scenario seems to be applicable for at least some Arctic organisms: insights into this problem emerged during the aquarium experiments.

Theme #2: .1, T3.3, T3.4, T3.5, T3.6, T3.8: During the project scientist involved in this work package took part in five scientific cruises. The ships used were as following r/v Oceania belonging to IO PAN, r/v GO Sars and r/v Johan Hjort both belonging to Institute of Marine Research in Norway. All of these cruises were in the Arctic covering such important areas as Norwegian, Barents and Greenland Sea. Extensive biological material for POL-NOR purposes was collected. At IO PAN mineralogical analysis of modern Arctic biota skeletons was continued. This was done with use of XRD (227 analysis has been done). In addition to this chemical elements composition was also analyzed with use of Inductively Coupled Plasma Mass Spectrometer (ICP-MS) (1760 analysis has been done). Wide range of biota was analysed including Crustacea, Asteroidea, Echinoidea, Ophiuroidea, Gastropoda, Bivalvia and Brachiopoda. These analyses covered not only screening of mineralogical and chemical composition of the shells on the species level but also large number of individuals within the species which allow us to recognize patterns of variability of various chemical elements between species, locations and environmental gradients occurring in the Arctic. Along biological samples also water samples were taken and analysed from the carbonate content point of view (saturation levels of aragonite, calcite). All these analyses combined enable to shown not only mineralogical and chemical composition of carbonate skeletons of Arctic biota but also link these to chemical and physical properties of the water column. Number of scientific papers were published out of these data (see section D for details).

Theme #3: T 3.2, T3.3, T3.4, T3.8: IP PAS scientific team completed assembly and upgrade of experimental aquaria (originally 4, upgraded to 6 fully controllable aquaria that allow for flexibility in planning the experiments). Aquaria are equipped with chiller, computer controller with auxiliary equipment (e.g., ion selective electrodes) for continuous measurements of the basic parameters of water. Two experiments with Arctic organisms were completed: (Ex1) The effect of ocean acidification on gastroliths development in American lobsters (Homarus americanus) and (Ex2) The effect of ocean acidification on shell development in common periwinkles (Littorina littorea).

(Re: Ex1) The aim of the first project was to investigate the effects of seawater acidification (pH 7.2 vs. 8.1 in control) on gastrolith development. These pH parameters were selected to represent the range of values from pre-industrial time until predicted conditions for the end of the current century. Only in normal pH conditions, cultured lobsters formed well developed gastroliths (developmental stages 2-3), whereas none were fully formed in animals cultured in acidified conditions (typically 0-1 stages). Assuming that similar shifts in timing of gastrolith formation may result from the worst-case scenario for anthropogenic ocean acidification, the lobster molting cycle, and consequently the lobster survival might be threatened (Conference publication Stolarski et al. 2017a,b; scheduled journal submission: 08-2017).

(Re: Ex2) The aim of the second project was to investigate biomineralization effects of reduced pH on shell formation of intertidal gastropod Littorina littorea. Common periwinkles were cultured at four different pH values: 7.4, 7.6, 7.8 and 8.1 (normal seawater pH, control tank) at near constant seawater temperature (10°C ±1°C) and salinity (34.5 ±1 PSU). L. littorea shells showed progressive surface corrosion along the pH gradient. Culturing in acidic pH has negative impact on periwinkle metabolism. Metabolic rates of cultured gastropods decrease from ~50% at pH 7.8 to ~10% at pH 7.4 in comparison with animals living at pH 8.2. The significant drop in basic metabolism was observed at the pH of 7.8. No significant change in growth dynamics were observed but fine-scale structural characteristic of the shell surface indicate that shell strength decreased by influence of acidified seawater. Such loss of structural integrity, resulting from both internal and external factors, may increase animal vulnerability to predation and to changing environment (paper in preparation: to be submitted by the end of 2017).

Another long-term taphonomic experiment (cooperation between IP PAN and IO PAN) will be continued beyond the time frame of the project. This experiment links a short-term with long-term, paleontological perspectives: calcium carbonate skeletons of all major representative groups of Arctic invertebrates are kept in aquaria (with and without influence of the sediment) at four different pH values: 7.4, 7.6, 7.8 and 8.1 (seawater temperature and salinity constant: 10°C ±1°C and 34.5 ±1 PSU, respectively. Changes in structural, mechanical and geochemical properties are measured and visualized (e.g., by computed tomography). The ultimate goal of this experiment is to present a model of skeletal changes (dissolution patterns/changes in mechanical properties) in major groups of Arctic invertebrates due to ocean acidification and assess the effects for fossilization potential. As such, the experiment may provide important explanatory took to understand biases in preservation of certain calcium carbonate fossils in the fossil record (end of experiment: 10-2017). Three (3 of 3) project deliverables were realized: (D 3.1) Database containing sediment, skeletal mineralogy combined with environmental parameters. Number of scientific papers were generated based on this database, these include Iglikowska et al. 2017a,b, Stolarski et al. 2016, Gothmann et al. 2015 – see section D for details. (D 3.2) Scientific manuscript on distributional patterns of skeletal mineralogy in relation to present carbonate saturation levels and other environmental factors in European boreal/Arctic waters [see section D for details: Iglikowska et al 2017a, b]; (D 3.3) Scientific manuscript on functional responses of skeletal growth, calcification, and mineralogy to variation in carbonate saturation state (number of publications are in advanced state and are scheduled for publication and will contribute to D.3.3 deliverable.