<sup>210</sup>Pb-<sup>226</sup>Ra chronology reveals rapid growth rate of <i>Madrepora oculata</i> and <i>Lophelia pertusa</i> on world's largest cold-water coral reef

Abstract

Abstract.Here we show the use of the 210 Ra excess method to determine the growth rate of two corals from the world's largest known cold-water coral reef, Røst Reef, north of the Arctic circle off Norway. Colonies of each of the two species that build the reef, Lophelia pertusa and Madrepora oculata, were collected alive at 350 m depth using a submersible. Pb and Ra isotopes were measured along the major growth axis of both specimens using low level alpha and gamma spectrometry and trace element compositions were studied. 210 Pb and 226 Ra differ in the way they are incorporated into coral skeletons. Hence, to assess growth rates, we considered the exponential decrease of initially incorporated 210 Pb, as well as the increase in 210 Pb from the decay of 226 Ra and contamination with 210 Pb associated with MnFe coatings that we were unable to remove completely from the oldest parts of the skeletons.226 Ra activity was similar in both coral species, so, assuming constant uptake of 210 Pb through time, we used the 210 Pb-226 Ra chronology to calculate growth rates. The 45.5 cm long branch of M. oculata was 31 yr with an average linear growth rate of 14.4 ± 1.1 mm yr −1 (2.6 polyps per year). Despite cleaning, a correction for Mn-Fe oxide contamination was required for the oldest part of the colony; this correction corroborated our radiocarbon date of 40 yr and a mean growth rate of 2 polyps yr −1 . This rate is similar to the one obtained in aquarium experiments under optimal growth conditions.For the 80 cm-long L. pertusa colony, metal-oxide contamination remained in both the middle and basal part of the coral skeleton despite cleaning, inhibiting similar age and growth rate estimates. The youngest part of the colony was free of metal oxides and this 15 cm section had an estimated a growth rate of 8 mm yr −1 , with high uncertainty (∼1 polyp every two to three years). We are less certain of this 210 Pb growth rate estimate which is within the lowermost ranges of previous growth rate estimates.We show that 210 Pb-226 Ra dating can be successfully applied to determine the age and growth rate of frameworkforming cold-water corals if Mn-Fe oxide deposits can be removed. Where metal oxides can be removed, large M. oculata and L. pertusa skeletons provide archives for studies of intermediate water masses with an up to annual time resolution and spanning over many decades.

In situ growth and bioerosion rates ofLophelia pertusain a Norwegian fjord and open shelf cold-water coral habitat

“…Highest extension rates of 15–17 mm yr −1 were obtained from aquarium cultivations of L. pertusa from the Mediterranean Sea (Orejas, Gori & Gili, 2008). In an elongated observation of this study, however, Orejas et al (2011) measured a mean linear extension rate of ∼ 9 mm yr −1 , which is in accordance with linear extensions measured of L. pertusa from different regions and through different analytical methods ranging from ~5.5 to 9.5 mm yr −1 (Mortensen, Rapp & Båmstedt, 1998; Mortensen, 2001; Roberts, 2002; Sabatier et al, 2012; Lartaud et al, 2013).…”

Decadal changes in the mid-depth water mass dynamic of the Northeastern Atlantic margin (Bay of Biscay)

“…Thus, the slight age difference (1-2 yr) assumed between the nodes of the branches and the ones of the corals trunk are within the age model uncertainty. The growth rate of 4.2 mm/yr for the M. oculata coral coincides with the lower values obtained from linear growth measurements performed in aquaria experiments with Mediterranean M. oculata specimens (between 3 and 18 mm/yr; Orejas et al, 2007Orejas et al, , 2011 and are also lower than the one recently measured by 210 Pb on a Norwegian specimen collected at 350 m depth (11-14 mm/yr; Sabatier et al, 2012). However, the Bay of Biscay is known for its patchy coral occurrences in canyons and along canyon heads.…”

Peer Review #3 of "In situ growth and bioerosion rates of Lophelia pertusa in a Norwegian fjord and open shelf cold-water coral habitat (v0.1)"

“…Highest extension rates of 15 -17 mm yr -1 were obtained from aquarium cultivations of L. pertusa from the Mediterranean Sea (Orejas et al, 2008). In an elongated observation of this study, however, Orejas et al (2011) measured a mean linear extension rate of about 9 mm yr -1 , which is in accordance with linear extensions measured of L. pertusa from different regions and through different analytical methods ranging from ~ 5.5 to 9.5 mm yr -1 (Mortensen & Rapp, 1998;Mortensen, 2001;Roberts, 2002;Sabatier et al, 2012;Lartaud et al, 2013).…”