Subarctic Rhodolith Beds Promote Longevity of Crustose Coralline Algal Buildups and Their Climate Archiving Potential

Abstract

The rocky, photic benthos of Arctic and Subarctic Biogeographic Regions has a characteristic seaweed flora that includes an extensive high-magnesium calcium carbonate basal layer of crustose coralline red algae. The thickest (10-40 cm) and oldest parts of the crust (previously reported as up to 640-830 years old), primarily at mid-photic depths of 15-25 m, are composed of buildups of the genus Clathromorphum. Due to its annual growth increments and cycling of Mg content with temperature, Clathromorphum has recently been developed as a high-resolution climate archive. The age of the archive is primarily limited by the boring of mollusks that reduce structural integrity, remove the record, and induce local diagenesis. Depressions and gentle slopes in the deeper portions of Subarctic rocky bottoms often collect mixed bioclastic and siliciclastic sediments, including a dense cover of rhodoliths (Lithothamnion glaciale and Lithothamnion tophiforme). In this paper we describe a transition zone of these two environments that forms on cobble/boulder glacial erratic bottoms in northern Labrador. Clathromorphum compactum buildups on the boulders and cobbles projecting through rhodolith beds can be preserved by finegrained anaerobic sediments that in turn reduce mollusk boring. This significantly enhances preservation and longevity of C. compactum crusts. We describe specimens of ages up to 1200 years BP, and discuss how greater ages can be obtained for archiving high-resolution climate information.

Anatomical structure overrides temperature controls on magnesium uptake – calcification in the Arctic/subarctic coralline algae <i>Leptophytum laeve</i> and <i>Kvaleya epilaeve</i> (Rhodophyta; Corallinales)

“…2b likely represents 4-5 years of vertical growth. At 80-100 µm of perithallial addition per year, this relates well to the 100-200 µm yr −1 found with extensive data in the same region for Clathromorphum compactum (Adey et al, 2015b).…”

“…November to July near-surface water temperatures, below the sea ice, are within the −1.5 to −1.8 • C range. Bottom summer temperature measured at the site on 22 July 2013 was 0.5 • C. Since this is relatively early in the summer season, peak temperatures are likely to be between 3 and 5 • C (Adey et al, 2015b) with a mean growing season temperature of ∼ 2 • C. This mean estimate is based on measurements from eight sites in the region (182 km S to 35 km N) with surface to bottom temperature records for 1964 (Adey, 1966c) and 2013 (Adey et al, 2015b). These ranged from 1.9 to 5.6 • C during summer at 15-20 m. The snow-covered land-fast sea ice overlying the gravel rhodolith bed from which the samples were taken likely precludes significant solar energy from reaching the bottom for 8 months of each year.…”

Amplification of the Atlantic Multidecadal Oscillation associated with the onset of the industrial-era warming

“…However all existing paleoclimate reconstructions that extend into the pre-industrial period are based on land-based proxies or tropical marine proxies15161718 and so there is concern that they may not fully capture variability in the AMO that has its largest amplitude and impact over the extra-tropical North Atlantic Ocean4814.…”

Phymatolithon (Melobesioideae, Hapalidiales) in the Boreal–Subarctic Transition Zone of the North Atlantic

“…More than 200 paraffin blocks of preserved specimens produced over 1,000 slides from which measurements and more than 200 micro-images were obtained; 30 SEM mounts were made that produced more than 250 images. For cell dimensions and other characters, the numbers of stations/plants/ filaments measured (i.e., for each data point) are as follows: Phymatolithon rugulosum, 25/41/52; P. laevigatum, 33/44/47; quantifiable, and statistically significant patterns of anatomy were identified; included was a newly described intercalary meristem (an uncommon feature in red algae) underlying the superficial morphology (Adey, 1964(Adey, , 1965Adey et al, , 2005Adey et al, , 2013Adey et al, , 2015a. The evolution of the diverse anatomy in these genera was hypothesized, in large measure, to be a defense against mollusk grazing (Steneck, 1982(Steneck, , 1992; different genera and species showed a wide variety of anatomical strategies to counter that grazing.…”

“…In deeper water, its sister species C. compactum maintains its conceptacles year after year, the conceptacles being buried, and often spores remain and are lost to reproductive potential. There is rarely a die-off, and the individual plants continuously occupy rock space for extended periods (typically to hundreds of years, but known to 1900 years; Adey et al, 2015a). Clathromorphum compactum occurs in a more stable environment, where competition for space by a host of encrusting invertebrates is extreme; once cover is established, it is more important to maintain that cover than to provide new spores, most of which will find few opportunities to settle.…”