Climate change projections for the surface ocean around New Zealand

<p>The future status of the surface ocean around New Zealand was projected using two Earth System Models and four emission scenarios. By 2100 mean changes are largest under Representative Concentration Pathway 8.5 (RCP8.5), with a +2.5°C increase in sea surface temperature, and decreases in surface mixed layer depth (15%), macronutrients (7.5–20%), primary production (4.5%) and particle flux (12%). Largest macronutrient declines occur in the eastern Chatham Rise and subantarctic waters to the south, whereas dissolved iron increases in subtropical waters. Surface pH projections, validated against subantarctic time-series data, indicate a 0.335 decline to ∼7.77 by 2100. However, projected pH is sensitive to future CO₂ emissions, remaining within the current range under RCP2.6, but decreasing below it by 2040 with all other scenarios. Sub-regions vulnerable to climate change include the Chatham Rise, polar waters south of 50°S, and subtropical waters north of New Zealand, whereas the central Tasman Sea is least affected.</p

Stable isotopic characteristics of post-trip whiskers for each sub-yearling elephant seal (n = 12).

*<p>Seals showed incomplete whisker growth (mm) during <i>in-utero</i>/lactation/fasting. Results for these animals are not included in the mean and overall mean (± standard deviation<b>).</b></p

Whisker δ¹³C and δ¹⁵N values of juvenile southern elephant seals from Macquarie Island.

<p>Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values from a randomly selected 2 mm section of whisker from (A) sub-yearling (n = 7; colour coded by foraging locations (IFZs) presented in Fig. 4), (B) one year (n = 35; light grey symbols), (C) two year (n = 40; dark grey symbols) and (D) three year old (n = 27; black symbols) age classes of elephant seals from Macquarie Island (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0086452#pone.0086452-Newland1" target="_blank">[75]</a>, this study). Also shown are marginal frequency distributions for the δ¹³C and δ¹⁵N values for each age class.</p

Schematic plots of δ¹³C and δ¹⁵N values along the post-trip whiskers of 12 sub-yearling southern elephant seals.

<p>We used stable carbon and nitrogen isotope values incorporated along the length of the whisker (mm). Values are colour-coded according to shift in food source along the temporal span of whisker presented in Fig. 1. Black symbols: <i>in-utero</i>/lactation/fasting; grey symbols: diet shift from mother’s milk and/or fasting to other food sources; open symbols: independent foraging at sea.</p

A schematic plot used to determine the shift to independent foraging along the post-trip whisker.

<p>We used stable nitrogen isotope values incorporated along the temporal span of the whisker as represented by the growth of the whisker from the distal (tip; oldest isotopic information) to proximal region (closest to the skin; most recent isotopic information). The red line indicates where the pre-trip basal segment (red symbol) intercepts δ¹⁵N values along the length of whisker. Solid arrows indicate the shift in food source along the temporal span from <i>in utero</i>/lactation to lactation/fasting (black symbols) to independent foraging at sea (open symbols). Dashed arrow indicates 3.9‰ drop in δ¹⁵N (equivalent to one trophic level ∼3.0‰; grey symbols). The first 14 mm of whisker represents independent foraging at sea.</p

Proportion of time spent (percentage) in Area Restricted Search (ARS) by seals in Inter-Frontal Zones (IFZs), including the Antarctic zone south of the southern Antarctic Circumpolar Current front-Southern Branch (S of SACCF-S), the ACC to Polar Front-Southern Branch (ACC to PF-S), the Polar Front (PF), the Polar Front to sub-Antarctic Front (PF to SAF) and the sub-Antarctic Front (SAF).

<p>The greatest proportion of seal ARS locations occurring in a particular IFZ defined their habitat group.</p

Tracks of 12 weaned southern elephant seals during their first migration from Macquarie Island.

<p>Tracks are colour-coded according to (A) behavioural state estimates from the two-state first-difference correlated random walk switching (DCRWS) model overlaid in yellow (Transit) and red (Area Restricted Search) and (B) Inter-Frontal Zones (IFZs). From south to north, IFZs included the Antarctic zone south of the southern Antarctic Circumpolar Current Front-Southern branch (S of SACCF-S), the ACC to Polar Front-Southern branch (ACC to PF-S), the PF, the PF to sub-Antarctic Front (PF to SAF), the SAF, and the SAF-Northern branch to sub-Antarctic Zone (SAF-N to SAZ). Dashed lines indicate the boundaries of CCAMLR Statistical Subareas 58.4.1, 88.1 and 88.2. All seal tracks originated and terminated at Macquarie Island, located in the South-West Pacific Ocean sector of the Southern Ocean.</p

Morphometric, tag deployment and tracking details for 12 weaned southern elephant seals from Macquarie Island, including the number of days (mean±SD) spent in transit and Area Restricted Search (ARS) by seals.

<p>Morphometric, tag deployment and tracking details for 12 weaned southern elephant seals from Macquarie Island, including the number of days (mean±SD) spent in transit and Area Restricted Search (ARS) by seals.</p