Hugh R. Grenfell

Morphological distinction of molecular types in Ammonia – towards a taxonomic revision of the world’s most commonly misidentified foraminifera

Abstract In this study, morphometric analysis has been performed on 178 Ammonia specimens belonging to 12 different molecular types, plus non-sequenced type specimens of Ammonia beccarii and A. tepida. Molecular type distinction is based on phylogenetic analysis of 267 partial LSU rDNA sequences, obtained from 202 living Ammonia specimens, sampled in 30 localities from 17 countries bordering the Pacific Ocean, Atlantic Ocean, Mediterranean Sea, Caribbean Sea and North Sea. Restriction fragment length polymorphism (analysis was carried out for another seven specimens. Morphometric analysis was based on measurements or assessments of 37 external test characters in spiral, umbilical, profile and close-up Scanning Electron Microscopic views. Cluster analysis, canonical variates analysis, and detrended correspondence analysis, performed on the morphological data set, suggest that each molecular type can be distinguished morphologically and can be regarded as a separate species. Primary types of A. tepida and topotypes of A. beccarii are shown to be morphologically separate from any of the molecular types so far recognised. We are aware of at least 9 more distinctive morphotypes that have not yet been sequenced, and thus we infer that the total number of genetically distinct and morphologically separable living species of Ammonia worldwide is likely to exceed 25–30. At this stage not all molecular types can be unequivocally assigned to formally described species. Several genetically-based species can be distinguished by the presence of one distinct character, but most are discriminated on the basis of a combination of many different characters. Morphological characters (e.g. test shape, chamber shape, porosity, prolocular diameter, folium shape, radial furrow length, umbilical diameter) are shown to be slightly more valuable in separating the molecular types than surficial ornament (beads, pustules, bosses, secondary calcite). One highly distinctive group (2–3 species – beccarii, batava, ?inflata) is readily discriminated on the basis of its large test size, strongly beaded and grooved ornament, and the presence of fissures along the sutures on the spiral side. The results of this study imply that the widespread practice of recognising only one, two or three species of Recent Ammonia worldwide should be abandoned. The most commonly used name, Ammonia beccarii, should be restricted to a large, compressed, highly ornamented species, so far not recognised beyond its type locality in the Adriatic Sea. Other commonly used names, such as A. parkinsoniana and A. tepida, apply to species with far more restricted distributions than the literature would suggest.

Tidal range of marsh foraminifera for determining former sea‐level heights in New Zealand

Abstract Quantitative study of live and total foraminiferal faunas in samples from six transects through marsh environments at Kaipara Harbour, Miranda, and Pauatahanui Inlet, New Zealand (two transects each), show the presence of a distinctive high tidal species association that has potential for the recognition of former sea‐level heights from late Quaternary deposits. Seven species associations are recognised by R‐mode cluster analysis of total (live plus dead) foraminiferal faunal data. Mangrove forest and salt meadow below MHWS (mean high water spring level), in near normal salinity marshes (Kaipara, Miranda), are dominated by an Ammonia association with subsidiary Elphidium excavatum, Haplophragmoides‐Miliammina fusca, and Helenina associations. In less saline marshes (Pauatahanui), the salt meadow and rush marsh below MHWS, are dominated by a Haplophragmoides‐Miliammina fusca association. In all transects, the narrow zone between MHWS and EHWS (extreme high water spring level) is dominated (>90% re...

Factors influencing the distribution patterns of Recent deep-sea benthic foraminifera, east of New Zealand, Southwest Pacific Ocean

Abstract This study investigates which combination of environmental factors most strongly influences the distribution patterns of benthic foraminferal tests (>0.63 μm) in a region bisected by the Subtropical Front, east of New Zealand. Seafloor sample sites extend from outer shelf (90 m) to abyssal (4700 m) depths, across substrates ranging from biogenic/terrigenous gravelly sand to hemipelagic mud, and occur under the influence of Antarctic intermediate water (AAIW) and circumpolar deep waters as well as receiving detritus from both Subtropical and Subantarctic surface water masses. Elevated values of the planktic foraminiferal fragmentation index and reworked small Paleogene planktic foraminifera at outer shelf and bathyal depths coincide with areas of strong bottom currents. Q-mode cluster analysis on the census counts of 398 benthic species clusters the 66 samples into three large groups (shallow, bathyal, abyssal), and at a lower level 10 mappable associations are recognised. A combination of canonical correspondence analysis and a correlation coefficient matrix was used to relate the faunal data to a set of measured environmental proxies. These analyses show that factors that have a relationship with depth are the most significant in determining foraminiferal distribution. The principal environmental factors which appear to most strongly influence this benthic foraminiferal distribution are: dissolved oxygen content in bottom waters; sustainability of organic carbon flux rates; seasonality of food supply; lateral advection of water masses; bottom water carbonate corrosiveness; energetic state at the benthic boundary layer; grain-size composition of substrate; salinity and temperature of the bottom waters. Shallow water associations (90–1250 m), dominated by Cassidulina carinata and Trifarina angulosa, occur within coarse substrates under well-oxygenated, high energy regimes and sustained food input. The occurrence of the bathyal associations (230–2840 m), dominated by C. carinata, Alabaminella weddellensis and Abditodentrix pseudothalmanni, closely mirrors the distribution of AAIW within a region of variable food supply. The sustainability of food supply combined with bottom water type and associated ventilation and dissolution strongly influence the composition of abyssal associations (1200–4700 m), mostly dominated by Epistominella exigua and A. weddellensis.

Depth distribution of recent deep-sea benthic foraminifera east of New Zealand, and their potential for improving paleobathymetric assessments of Neogene microfaunas

Abstract Paleobathymetric assessments of fossil foraminiferal faunas play a significant role in the analysis of the paleogeographic, sedimentary, and tectonic histories of New Zealands Neogene marine sedimentary basins. At depths >100 m, these assessments often have large uncertainties. This study, aimed at improving the precision of paleodepth assessments, documents the present‐day distribution of deep‐sea foraminifera (>63 μm) in 66 samples of seafloor sediment at 90–4700 m water depth (outer shelf to mid‐abyssal), east of New Zealand. One hundred and thirty‐nine of the 465 recorded species of benthic foraminifera are new records for the New Zealand region. Characters of the foraminiferal faunas which appear to provide the most useful information for estimating paleobathymetry are, in decreasing order of reliability: relative abundance of common benthic species; benthic species associations; upper depth limits of key benthic species; and relative abundance of planktic foraminifera. R‐mode cluster analysis on the quantitative census data of the 58 most abundant species of benthic foraminifera produced six species associations within three higher level clusters: (1) calcareous species most abundant at mid‐bathyal to outer shelf depths (<1000 m); (2) calcareous species most abundant at mid‐bathyal and greater depths (>600 m); (3) agglutinated species mostly occurring at deep abyssal depths (>3000 m). A detrended correspondence analysis ordination plot exhibits a strong relationship between these species associations and bathymetry. This is manifest in the bathymetric ranges of the relative abundance peaks of many of the common benthic species (e.g., Abditodentrix pseudothalmanni 500–2800 m, Bolivina robusta 200–650 m, Bulimina marginata f. marginata 20–600 m, B. marginata f. aculeata 400–3000 m, Cassidulina norvangi 1000–4500 m, Epistominella exigua 1000–4700 m, and Trifarina angulosa 10–650 m), which should prove useful in paleobathymetric estimates. The upper depth limits of 28 benthic foraminiferal species (e.g., Fursenkoina complanata 200 m, Bulimina truncana 450 m, Melonis affinis 550 m, Eggerella bradyi 750 m, and Cassidulina norvangi 1000 m) have potential to improve the precision of paleobathymetric estimates based initially on the total faunal composition. The planktic percentage of foraminiferal tests increases from outer shelf to upper abyssal depths followed by a rapid decline within the foraminiferal lysocline (below c. 3600 m). A planktic percentage <50% is suggestive of shelf depths, and >50% is suggestive of bathyal or abyssal depths above the CCD. In the abyssal zone there is dramatic taphonomic loss of most agglutinated tests (except some textulariids) at burial depths of 0.1–0.2 m, which negates the potential usefulness of these taxa in paleobathymetric assessments.

Faunal changes in Waitemata Harbour sediments, 1930s‐1990s

A resurvey of Powells classic study of subtidal, soft‐bottom communities in the Waitemata Harbour, Auckland, was undertaken to determine the nature of faunal changes between the 1930s and 1990s. Samples were dredged and associations were intuitively deduced largely on the basis of molluscs and echinoderms, in a similar fashion to Powells 1930s study. Away from the wharves and marinas the soft‐bottom fauna is still remarkably rich and diverse, and retains a similar gross pattern to the 1930s. Fourteen mollusc species (dominantly carnivorous gastropods) appear to have disappeared or suffered major reductions in abundance within the harbour. This has resulted in the disappearance of two of Powells associations (Tawera‐Tucetona, Amalda) from the outer harbour. There has also been an apparent reduction in the abundance and range of the turritellid Maoricolpus roseus and a number of associated species of the shelly channel sediments in the centre of the harbour. Since the 1930s at least nine New Zealand moll...

Benthic foraminiferal proxy evidence for the Neogene palaeoceanographic history of the Southwest Pacific, east of New Zealand

Abstract Canonical correspondence analysis indicates that the distribution of Neogene benthic foraminiferal faunas (>63 μm) in seven DSDP and ODP sites (500–4500 m water depth) east of New Zealand (38–51°S, 170°E–170°W) is most strongly influenced by depth (water mass stratification), and secondly by age (palaeoceanographic changes influencing faunal composition and biotic evolution). Stratigraphic faunal changes are interpretted in terms of the pulsed sequential development of southern, and later northern, polar glaciation and consequent cooling of bottom waters, increased vertical and lateral stratification of ocean water masses, and increased overall and seasonal surface water productivity. Oligocene initiation of the Antarctic Circumpolar Current and Deep Western Boundary Current (DWBC), flowing northwards past New Zealand, resulted in extensive hiatuses throughout the Southwest Pacific, some extending through into the Miocene. Planktic foraminiferal fragmentation index values indicate that carbonate dissolution was significant at abyssal depths throughout most of the Neogene, peaking at upper abyssal depths in the late Miocene (11–7 Ma), with the lysocline progressively deepened thereafter. Miocene abyssal faunas are dominated by Globocassidulina subglobosa and Oridorsalis umbonatus , with increasing Epistominella exigua after 16 Ma at upper abyssal depths. Peak abundances of Epistominella umbonifera indicate increased input of cold Southern Component Water to the DWBC at 7–6 Ma. Faunal association changes imply establishment of the modern Oxygen Minimum Zone (upper Circumpolar Deep Water) in the latest Miocene. Significant latitudinal differences between the benthic foraminiferal faunas at lower bathyal depths indicate the existence of an oceanic front along the Chatham Rise (location of present Subtropical Front), since the early late Miocene at least, with more pulsed productivity (higher E. exigua ) along the south side. Modern Antarctic Intermediate Water faunal associations were established north of the Chatham Rise at 10–9 Ma, and south of it at 3–1.5 Ma. Middle–upper bathyal faunas on the Campbell Plateau are dominated by reticulate bolivinids during the early and middle Miocene, indicative of sustained productivity above relatively sluggish, suboxic bottom waters. Faunal changes and hiatuses indicate increased current vigour over the Campbell Plateau from the latest Miocene on. Surface water productivity (food supply) appears to have increased in three steps (at times of enhanced global cooling) marked by substantially increased relative abundance of: (1) Abditodentrix pseudothalmanni , Alabaminella weddellensis , Cassidulina norvangi (16–15 Ma, increased pulsed productivity); (2) Bulimina marginata f. aculeata , Nonionella auris , Trifarina angulosa , Uvigerina peregrina (3–1.5 Ma, increased overall productivity); and (3) Cassidulina carinata (1–0.5 Ma, increased overall productivity). Three intervals of deep-sea benthic foraminiferal taxonomic turnover are recognised (16–15, 11.5–10, 2–0.5 Ma) corresponding to intervals of enhanced global cooling and possible productivity changes. The late Pliocene–middle Pleistocene extinction, associated with increasing Northern Hemisphere glaciation, culminating in the middle Pleistocene climatic transition, was more significant in the study area than the earlier Neogene turnovers.

Effect and timing of increased freshwater runoff into sheltered harbor environments around Auckland City, New Zeland

Two short cores of late Holocene, low tidal, estuarine sediment from the sheltered fringes of the Aucklands Waitemata Harbor, New Zealand, record the following changes through time since human colonization: an abrupt decline and disappearance of marine molluscs, a major decline and virtual disappearance of ostracods, an abrupt decline in calcareous foraminifera (mostlyAmmonia spp.), a rapid increase, in abundance of agglutinated foraminifera, large diatoms, and freshwater thecamoebians, and an increase in sedimentation rate, but no consistent trend in change of grain size. The up-core foraminiferal changes mimic their present day up-estuary zonation, which correlates strongly with decreasing salinity and pH. In both localities the faunal changes can be correlated with the documented local land-use history and increased freshwater runoff over time. At the head of the Waitemata Harbor, in Lucas Creek estuary, three phases of foraminiferal faunal change occurred: minor changes during initial Polynesian forest clearance (1500–1800 AD), a major change in early European times (1840–1870 AD) with clearance of most of the remaining native forest, and another small change in very, recent times (∼1990s) with urbanization in the Lucas Creek catchment. On the eastern, seaward fringes of the Waitemata Harbor, in the smaller Tamaki Estuary, no faunal changes occurred in association with complete forest clearance and establishment of pastoral farming in Polynesian and early European times (before 1950s). Major foraminiferal and other faunal changes occurred in the late European period (1960s–1970s) coincident with the onset of major urbanization spreading throughout the Tamaki catchment. Our results suggest increased freshwater runoff is the major culprit for many of the observed biotic changes in the urbanized estuaries of New Zealand.

Foraminiferal and molluscan evidence for the Holocene marine history of two breached maar lakes, Auckland, New Zealand

Abstract Drillhole records of fossil Foraminifera and Mollusca, together with sparse tephra age control, document similar Holocene marine histories of two of Aucklands breached maars—Pukaki Lagoon, Manukau Harbour, and Onepoto Lagoon, Waitemata Harbour. Following eruption, both maars slowly accumulated carbonaceous mud in freshwater lakes, until they were breached by rising sea level in the early Holocene (c. 8100 cal. yr at Onepoto, c. 7600 cal. yr at Pukaki). Following breaching, both became saltwater tidal lagoons with silled, subtidal basins rapidly accumulating marine mud as the underlying sediment compacted. Onepoto Lagoon may have had deeper water than Pukaki, because it was colonised by a foraminiferal fauna (Bolivina, Bulimina, Buliminella, Spiroloxostoma) that prefers quiet, dysoxic bottom conditions. Both fossil groups identify where the lagoons shallowed from subtidal to low tidal depths. This occurs c. 15 m downhole (6900 cal. yr) in Pukaki and c. 9.5 m downhole in Onepoto, after sea‐level rise had levelled off at about its present height (7000 cal. yr). Marine mud sedimentation slowed in the intertidal, accumulating largely in response to 12 m and 5 m compaction of the maar fill, respectively. Subtidal and low tidal fringe foraminiferal faunas of both lagoons are characterised by Ammonia‐Haynesina associations, whereas intertidal faunas above mean low water are dominated (>90%) by Ammonia. Pukaki Lagoon foraminiferal faunas differ from Onepoto by their higher subtidal diversity of benthic foraminiferal tests and the presence of planktic tests in the subtidal section. These differences are inferred to relate to the significantly more exposed conditions outside the entrance to Manukau Harbour, where juvenile benthic tests were lifted into suspension and, together with the planktics, carried by the strong tidal currents up the harbour channels into Pukaki Lagoon. These introduced tests settled out of suspension in the quiet subtidal waters and accumulated in the sediment. Once Pukaki Lagoon had been filled with mud to intertidal depths, most introduced tests were apparently flushed away by the outgoing tides and did not accumulate. The presence in the Onepoto sequence (9.8–8.7 m) of the gastropods Micrelenchus huttonii and Notoacmea helmsi f. scapha indicate that Zostera seagrass once grew in the lagoon at around spring low tide level.

Microfossil record of the Holocene evolution of coastal wetlands in a tectonically active region of New Zealand

The shallow tidal Wairau coastal lagoons, New Zealand, are in a prime location for investigating the relative roles of tectonic and eustatic sea level on their palaeogeographic evolution. The Wairau lagoons are unique in New Zealand for their wide seasonal and tidal salinity range, from hyposaline (10—20 psu) to hypersaline (35—54 psu). Foraminiferal and ostracod associations are recognised, using Q-mode cluster analysis, living in and around these lagoons and detrended canonical correspondence analysis (DCCA) shows that their distributions are strongly correlated with tidal elevation and salinity. Analyses of the modern analogue faunal data combined with Holocene microfaunal data from five 2.5—9 m deep cores enables direct palaeoenvironmental interpretation of the fossil faunas and elucidation of the lagoons’ palaeogeographic evolution. The area was inundated by rising eustatic sea level from 8.5 ka onwards, forming a fully marine, sheltered, subtidal bay. Sediment supply outpaced local tectonic subsidence and the bay filled with mud, shallowing to intertidal by 4.5—3.5 ka, still with an open mouth to the sea. Since then sediment supply has kept pace with 3—4 m of inferred tectonic subsidence. At ~1.5 ka the calcareous-dominated foraminiferal faunas suddenly changed to agglutinate-dominated faunas, indicating a switch to a semi-closed lagoon linked to the Wairau River estuary, with highly varied salinity like today. We infer this was caused by northwards extension of the Wairau Boulder Bank across the bay’s mouth in response to a sharp eustatic sea-level fall after 2 ka. Sediment supply switched to fluvially derived sand which built a flood-delta into the lagoon dividing it into three water bodies. Relative sea-level rise in the last 600 years from earthquake-related compaction (AD 1855) and accelerating eustatic rise (0.6 m) has resulted in increased marginal erosion of the lagoons and their re-amalgamation into one linked water body.

Recent benthic foraminifera from offshore Taranaki, New Zealand

Abstract Paleobathymetric estimates based on fossil foraminiferal faunas play an important role in understanding the paleogeographic, structural, and burial history of New Zealands most important hydrocarbon‐bearing sedimentary basin—the Taranaki Basin. Bathyal and abyssal estimates have large ranges of uncertainty, which might be improved using knowledge of the depth distribution patterns of Recent benthic foraminifera in the same region. Four benthic foraminiferal groups (and 9–10 associations) are recognised and mapped in the offshore Taranaki region (0–2150 m depth, eastern Tasman Sea), based on two separate cluster analyses of census data (231 species, 39 samples) on faunas with tests >63 and >150 μm. The same depth pattern can be identified using 63 or 150 μm faunas, although there are major differences in the dominant taxa. Canonical correspondence analysis and correlation coefficients suggest that the distribution patterns are strongly depth related: (1) inner shelf (0–50 m) associations (both shell‐size fractions) are dominated by Rosalina irregularis and Zeaflorilus parri; (2) outer shelf‐uppermost bathyal (50–550 m) associations are dominated by Bulimina marginata s.s. and Discorbinella bertheloti (both sizes) plus Cassidulina carinata (>63 μm) or Cibicides dispars (>150 μm); (3) middle‐lower bathyal (500–1500 m) associations are dominated by C. carinata‐Alabaminella weddellensis‐Abditodentrixpseudothalmanni (>63 μm) and Uvigerina peregrina‐Bulimina marginata f. aculeata (>150 μm); and (4) lower bathyal to upper abyssal (1400–2150 m) associations are dominated by B. marginata f. aculeata and Globocassidulina subglobosa (both) plus A. weddellensis (>63 μm) or U. peregrina‐Oridorsalis umbonatus (>150 μm). Comparison of the >63 μm Taranaki (west coast) faunal data with a similar dataset from east of New Zealand shows significant differences in composition, relative abundance levels, and depth ranges of common species, which appear to be a result of differences in primary productivity, translated into organic carbon flux (food). Since organic carbon flux reaching the seafloor decreases progressively with increasing water depth, we infer that this is the major factor producing the strong depth‐related distributional pattern of deep‐sea benthic foraminiferal faunas observed around New Zealand. Thus, highly accurate estimates of paleobathymetry are unlikely using benthic foraminifera, unless organic carbon flux has remained unchanged. Notwithstanding the differences between the west and east coasts, there are sufficient similarities and trends that are bathymetrically consistent to be useful in improving paleobathymetric estimates. These include, in decreasing order of reliability: upper depth limits of key benthic species; recognition of benthic foraminiferal associations; and relative abundance of planktic foraminifera. Species diversity measures show no useful pattern with depth.