A marine to freshwater sediment succession from Kowhai Beach wetland, Northland: Implications for Holocene sea level

Abstract

An infilled wetland located behind coastal dunes in north‐east Northland is used to reconstruct a local history of environmental change spanning early Holocene (c. 7000 yr BP) to modern time. Proxy indicators (sediment texture, diatoms and pollen) provide evidence for a transition from marginal marine‐ to brackish‐ to freshwater‐conditions in the wetland. Radiocarbon ages constrain the chronology of this succession to 7880–7430 cal. yr BP for the early period of marine conditions, 3570–3210 cal. yr BP for the latter brackish phase and 1060–800 cal. yr BP for the change to freshwater conditions. Within this succession, the diatom record preserves a strong brackish signal at core depths above the limit of the modern tidal range. This is presented as preliminary evidence for a mid‐Holocene sea level highstand for northern New Zealand of approximately 1.2 m above present mean sea level.

Keywords:

• diatoms
• ¹⁴C dating
• highstand
• palynology
• sea level
• sediments
• stratigraphy

Notes

School of Geography, Geology and Environmental Science, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand.