Subsidence-driven environmental change in three Holocene embayments of Ahuriri Inlet, Hikurangi Subduction Margin, New Zealand

We use 295 foraminiferal samples from 45 short cores (up to 8 m deep) to reconstruct the paleoenvironmental history of the bays. We infer that the strongest influence on their paleoenvironmental history was 8–10 m of net tectonic subsidence since 7.3 ka, which provided the accommodation space for sediment deposition prior to the c. 1.5 m of uplift in the AD 1931 Hawkes Bay Earthquake.

Much of the subsidence appears to have occurred in eight large co-seismic events (0.4–2 kyr recurrence time) which caused marine transgressions of varying amounts into each bay. Sea-level changes (eustatic and isostatic) have been a secondary driver over the middle–late Holocene with an interval (c. 2.6–1.7 ka) of widespread erosion or slow sedimentation, caused by a sea-level fall of c. 1 m following the middle Holocene highstand.