Utility of Dendrochronology Crossdating Methods in the Development of Arctic Coralline Red Algae Clathromorphum compactum Growth Increment Chronology for Sea Ice Cover Reconstruction

Abstract

Paleoclimate and paleoenvironmental reconstructions from increment-yielding archives strongly depend on precise age models. Like bivalves, corals, trees, and speleothems, the coralline alga Clathromorphum compactum produces annual growth increments and shows considerable promise as an environmental archive for arctic and subarctic regions. Though their growth increment widths correlate with temperature and sea ice cover in high Arctic regions, existing timeseries have not been crossdated. In fact, previous studies have shown a lack of inter-sample correlation in non-crossdated timeseries suggesting possible age model dating errors. Here, we use dendrochronology crossdating techniques and COFECHA software to ensure and validate synchrony between C. compactum timeseries (<141 years) from three specimens collected near Beechey Island, Nunavut, Canada. Results showed that non-crossdated timeseries constructed by four coralline red algae researchers using annual increments of the same C. compactum samples were highly variable and showcase the likelihood of dating errors in non-crossdated timeseries. Crossdating improved inter-series correlations, and correlations to sea ice-related records, suggesting that at least three crossdated timeseries are required to isolate paleoclimate signals. Our findings suggest that future reconstructions with C. compactum should employ crossdating techniques to reduce dating errors and allow for more precise climate reconstructions.Lay AbstractLong-term environmental records provide a critical baseline to examine how humans have impacted Earth’s natural climate. An important piece to consider is sea ice’s role in natural climate variability because its brightness limits warming by reflecting solar irradiation back to space. However, instrumental records of sea ice rarely extend beyond the early satellite era (late 1970s), limiting our understanding of how sea ice affects natural climate variability in the preindustrial era. A lack of historical baseline prompted the development of sea ice proxies, including the long-lived marine alga, Clathromorphum compactum. Similar to tree-rings, C. compactum produces a new mineralized layer each year, and layer thicknesses have been shown to respond to sea ice cover, making them useful to record long-term sea ice variability. However, a recent study showed that records had replicability problems, maybe due to dating mistakes. Our study applies tree-ring dating methods (dendrochronology) to match annual algal growth layers across algal specimens. Results showed that these new methods reduced dating errors, allowing for more precise past sea ice cover reconstructions.

Growth Increments of Coralline Red Alga Clathromorphum Compactum Capture Sea‐Ice Variability Links to Arctic and Atlantic Multidecadal Oscillations (1805–2015)

“…Right plot shows Beechey Island region enlarged. (b) Plotted algal growth increment timeseries (black: anomalies = (annual value − average)/standard deviation) and NSIDC sea‐ice concentrations (blue: 75 km 2 around Beechey Island site) (see Leclerc et al., 2022 for original figure of subplot B). Growth anomalies are plotted inversely.…”

“…Line scans were ablated (5 μm/second) along the growth axis, using an aperture size of 10 × 70 μm, and a 10 Hz laser pulse rate ( see details in Hetzinger et al., 2011). Age models were constructed with crossdating methods (Leclerc et al., 2022; Text S1 in Supporting Information ). In addition, prior to 1880, only sample 41, providing the longest continuous chronology, was used to extend the record back to 1805.…”

“…To date, several coralline‐algal‐sea‐ice‐proxy (CASIP) records have been produced from C . compactum samples collected in the Arctic (Halfar et al., 2013; Hetzinger et al., 2019a; Leclerc et al., 2022; Moore et al., 2017). In this study, we show that C .…”

Growth as a function of sea ice cover, light and temperature in the arctic/subarctic coralline C. compactum: A year-long in situ experiment in the high arctic

“…The strong relationship between year-to-year variability in annual sea-ice extent and algal growth has allowed for the reconstruction of sea-ice variability in the High Arctic through time using a combination of both skeleton growth band anomalies and Mg/Ca anomalies in this species through time (Halfar et al, 2013;Hetzinger et al, 2019;Leclerc et al, 2022a;Leclerc et al, 2022b). Leclerc et al (2022b) for instance, find strong correlations between growth band thickness (growth anomalies) and summer sea-ice concentrations in three crossdated specimens of C. compactum from Beechey Island, Nunavut.…”

“…The strong relationship between year-to-year variability in annual sea-ice extent and algal growth has allowed for the reconstruction of sea-ice variability in the High Arctic through time using a combination of both skeleton growth band anomalies and Mg/Ca anomalies in this species through time (Halfar et al, 2013;Hetzinger et al, 2019;Leclerc et al, 2022a;Leclerc et al, 2022b). Leclerc et al (2022b) for instance, find strong correlations between growth band thickness (growth anomalies) and summer sea-ice concentrations in three crossdated specimens of C. compactum from Beechey Island, Nunavut. However, the laboratory experiment of Williams et al (2018) also illustrates that light availability may have a large control not only on the growth and calcification of this marine alga, as previously illustrated, but also on the incorporation of Mg/Ca into the skeleton, adding uncertainty to the Mg/Ca proxy for reconstructing both seawater temperature and sea-ice extent.…”