Marine radiocarbon (14C) ages are an important geochronology tool for the understanding of past earthquakes and tsunamis that have impacted the coastline of New Zealand. To advance this field of research, we need an improved understanding of the radiocarbon marine reservoir correction for coastal waters of New Zealand. Here we report 170 new ΔR20 (1900–1950) measurements from around New Zealand made on pre-1950 marine shells and mollusks killed by the 1931 Napier earthquake. The influence of feeding method, living depth and environmental preference on ΔR is evaluated and we find no influence from these factors except for samples living at or around the high tide mark on rocky open coastlines, which tend to have anomalously low ΔR values. We examine how ΔR varies spatially around the New Zealand coastline and identify continuous stretches of coastline with statistically similar ΔR values. We recommend subdividing the New Zealand coast into four regions with different marine reservoir corrections: A: south and western South Island, ΔR20 –113 ± 33 yr, B: Cook Strait and western North Island, ΔR20 –171 ± 29 yr, C: northeastern North Island, ΔR20 –143 ± 18 yr, D: eastern North Island and eastern South Island, ΔR20 –70 ± 39 yr.

Spermaceti is a waxy substance found in the head cavities of sperm whales (Physeter macrocephalus and P. catodon). This substance had a variety of commercial applications from the end of the 18th to the beginning of the 20th century, such as candles, soap, cosmetics and other compounds. Spermaceti was also occasionally used as wax for modeling sculptures. In order to date such artworks the marine reservoir effect (MRE) has to be considered. The chemical library of the Muséum national d’Histoire naturelle (Paris, France) contains samples of spermaceti studied by the French chemist M. E. Chevreul (1786–1889) at the beginning of the 19th century. Eight samples of substances preserved in their original containers were 14C dated. According to the whaling practices and the publications of Chevreul, we estimated that the spermaceti samples came from whales caught between 1805 and 1815. AMS 14C dating results are from 550 to 1180 ± 30 BP, R values between 393 and 1023 (± 34) 14C yr and ΔR between –168 and 504 (± 60) 14C yr. The values presented here are the first ever obtained for spermaceti. However, being based on museum specimens, further measurements on crude material would be necessary to refine these results.

Radiocarbon ages on mollusk shells, which account for about half of the more than 8,000 dates from cultural deposits on the west coast of North America, need to be corrected for the local marine reservoir effect (ΔR) to yield true ages. Assays on “prebomb” shells show that ΔR increases poleward, echoing the age gradient in offshore waters. The meridional gradient in ΔR is not appreciably affected by the transition either from an upwelling regime to a downwelling regime north of 40°N–45°N or from a winter maximum-high alkalinity river discharge pattern to a summer maximum-low alkalinity pattern at the same latitude, probably because these changes are offset by increasing storminess and tidal energy in coastal areas. Mesoscale variations in ΔR along this gradient are attributable to contrasts in shore morphology and exposure. Data from 123 shell-wood pairs reveal similar patterns of temporal variation in ΔR in the late Holocene in the coastal ecoregions. The characteristic temporal pattern echoes phases of variable El Niño-Southern Oscillation (ENSO) activity. The high degree of variability in ΔR argues against the indiscriminate application of regionally uniform or trans-Holocene ΔR values and demands improvements in spatiotemporal resolution if shell is used to date cultural deposits.

To identify chronological changes in the marine reservoir effect in southwest Japan, the radiocarbon ages of eight pairs of marine shells and terrestrial plants were measured from the same horizons of one core of Holocene sediments. This core was obtained from the northern part of the Sukumo Plain in southwestern Shikoku Island, which faces the warm Kuroshio Current. The drilling site is located in an area of subsidence associated with the convergence of the Philippine Sea Plate and the Eurasian Plate. On analyses of lithology, molluscan assemblages, and radiocarbon dating, we interpreted, from oldest to youngest, nine units: basement rock, a braided river channel, a meandering river channel, an estuary, a transgressive inner bay, Kikai-Akahoya volcanic ash, a deltaic inner bay, a tidal flat, and artificial soil. Changes in the depositional environment were mainly associated with sea-level rise after the end of the last glaciation. The reservoir ages of the eight pairs, 330 ± 70 yr, were obtained from a transgressive inner bay to deltaic inner bay sediments, formed during 4100–9200 cal BP. The chronological change in the reservoir effect allows us to correlate the Sukumo Core sediments with previous results from southwestern Japan, the Korean Peninsula, and Taiwan Island.

To investigate the relationship between paleoenvironmental changes and marine reservoir effects, the radiocarbon ages of marine bioclasts and terrestrial plants from the same horizons of a sediment core in the Holocene Epoch were measured. This core, with a length of approximately 9 m, was obtained from the southern part of the Miyazaki Plain southeast of Kyushu Island, which faces the Kuroshio warm current. This drilling site is located in an uplift area associated with the subduction of the Philippine Sea Plate. Based on analyses of lithology, molluscan and foraminifera assemblages, and radiocarbon dating, we interpreted four sedimentary units in order of age: tidal flat, inner bay, Kikai-Akahoya volcanic ash, and delta plain. These paleoenvironmental changes were mainly associated with the sea-level rise during the deglacial period. The reservoir ages of nine pairs from the tidal flat to inner bay facies were found to be from the time span of 7300–8200 cal BP. The chronological changes in the reservoir effect are correlated with those seen in Holocene sediments of the other coastal area in East Asia.

Beppu Bay is located on east-central Kyushu, southwest Japan, and is characterized by hydrothermal activity, tectonic deformation, and recent volcanism under the influence of convergence of the Philippine Sea plate. This area, occupying the western portion of an arc-bisecting dextral fault system, is a tectonic depression that has existed since ca. 5 Ma. Sedimentary facies, mollusk assemblages, and radiocarbon (14C) ages of 25 terrestrial plant fragments and 16 marine carbonate shells from a 70-m drill core were determined to estimate the activity of the Funai Fault, which consists of normal faults along the southern margin of the tectonic basin. Based on the analysis, six sedimentary facies, namely braided river channel, estuary, prodelta, delta front, delta plain, and artificial soil, were identified. The vertical slip rate was calculated as 2.6–2.7 mm/yr based on displacements of the braided river channel sediments of the last glacial period and the base of Kikai-Akayoya tephra in the Holocene highstand sediments of this area. Reservoir ages during 6180–10,410 cal BP were determined from marine shell and terrestrial plant pairs from the sediments of the estuary, prodelta and delta front facies, and were correlated with values from a northern coast of Kyushu and the Korean Peninsula.