Methane Seepage Along the Hikurangi Margin, New Zealand

ARTICLE IN PRESS MARGO-04469; No of Pages 20 Marine Geology xxx (2010) xxx–xxx

Contents lists available at ScienceDirect

Marine Geology

journal homepage: www.elsevier.com/locate/margeo

Methane seepage along the Hikurangi Margin, New Zealand: Overview of studies in 2006 and 2007 and new evidence from visual, bathymetric and hydroacoustic investigations

J. Greinert a,b,⁎, K.B. Lewis c, J. Bialas b, I.A. Pecher d, A. Rowden c, D.A. Bowden c, M. De Batist a, P. Linke b a Renard Centre of Marine Geology (RCMG), Ghent University, Krijgslaan 281 s.8, B-9000 Gent, Belgium b IFM-GEOMAR, Leibniz Institute of Marine Sciences at the University of Kiel, Wischhofstraße 1-3, 24148 Kiel, Germany c National Institute of Water and Atmospheric Research, Private Bag 14 901, Kilbirnie, Wellington, New Zealand d GNS Science, 1 Fairway Drive, Avalon, Lower Hutt 5010, New Zealand article info abstract

Article history: This paper is an introduction to and an overview of papers presented in the Special Issue of Marine Geology Received 5 May 2009 “Methane seeps at the Hikurangi Margin, New Zealand”. In 2006 and 2007, three research cruises to the Received in revised form 20 December 2009 Hikurangi Margin at the east coast of New Zealand's North Island were dedicated to studying methane Accepted 23 January 2010 seepage and gas hydrates in an area where early reports suggested they were widespread. Two cruises were Available online xxxx carried out on RV TANGAROA and one on RV SONNE using the complete spectrum of state-of-the-art equipment for geophysics (seismic, sidescan, controlled source electromagnetics, ocean bottom seism- Keywords: fl methane seepage ometers and hydrophones, singlebeam and multibeam), sea oor observations (towed camera systems, gas hydrate ROV), sediment and biological sampling (TV-guided multi-corer, gravity-corer, grab, epibenthic sled), multibeam mapping deployment of in-situ observatories (landers) as well as water column sampling and oceanographic studies hydroacoustic flares (CTD, moorings). The scientific disciplines involved ranged from geology, geophysics, petrography, Hikurangi Margin geochemistry, to oceanography, biology and microbiology. New Zealand These cruises confirmed that a significant part of the Hikurangi Margin has been active with locally intense methane seepage at present and in the past, with the widespread occurrence of dead seep faunas and knoll- forming carbonate precipitations offshore and on the adjacent land. A close link to seismically detected fluid systems and the outcropping of the base of the gas hydrate stability zone can be found at some places. Pore fluid and free gas release were found to be linked to tides. Currents as well as density layers modulate the methane distribution in the water column. The paper introduces the six working areas on the Hikurangi Margin, and compiles all seep locations based on newly processed multibeam and multibeam backscatter data, water column hydroacoustic and visual data that are combined with results presented elsewhere in this Special Issue. In total, 32 new seep sites were detected that commonly show chemoherm-type carbonates or carbonate cemented sediment with fissures and cracks in which calyptogenid clams and bathymodiolid mussels together with sibloglinid tube worms live. White bacterial mats of the genus Beggiatoa and dark gray beds of heterotrophic ampharetid polychaetes typically occur at active sites. Bubble release has frequently been observed visually as well as hydroacoustically (flares) and geochemical analyses show that biogenic methane is released. All seep sites, bubbling or not, were inside the gas hydrate stability zone. Gas hydrate itself was recovered at three sites from the seafloor surface or 2.5 m core depth as fist-sized chunks or centimeter thick veins. The strong carbonate cementation that in some cases forms 50 m high knolls as well as some very large areas being paved with clam shells indicates very strong and long lasting seep activity in the past. This activity seems to be less at present but nevertheless makes the Hikurangi Margin an ideal place for methane-related seep studies in the SW-Pacific. © 2010 Elsevier B.V. All rights reserved.

1. Introduction

1.1. Cold seeps

⁎ Corresponding author. Now at Royal Netherlands Institute for Sea Research, P.O. ﬂ Box 59 , NL-1790 AB Den Burg, The Netherlands. Submarine cold seeps are sites where uids, both pore water and E-mail address: [email protected] (J. Greinert). free gas, migrating from deeper sediment horizons, are expressed

Please cite this article as: Greinert, J., et al., Methane seepage along the Hikurangi Margin, New Zealand: Overview of studies in 2006 and 2007 and new evidence from visual, bathym..., Marine Geology (2010), doi:10.1016/j.margeo.2010.01.017 ARTICLE IN PRESS

2 J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx from the seabed into the overlying water column (Suess, 2010). They takes place along the 3000 m deep, infilled structural trench of the are often inferred to be associated with gas hydrates in the underlying Hikurangi Trough, along the toe of the slope (Lewis et al., 1998). sediment, which can act as time-variable sources or sinks for The central part of the margin is characterized by a particularly methane, the dominant gas component at most seeps. Methane, well defined accretionary prism of imbricated, offscraped Plio- together with hydrogen sulphide that is expelled at some seep sites, Pleistocene “trench” turbidites from the Hikurangi Trough (Lewis, allow chemoautotrophic faunas to thrive, and cause precipitation of 1980; Davey et al., 1986a, b; Barnes and Mercier de Lepinay, 1997; methane-derived authigenic carbonates at the sea floor, which can Barnes et al., 2009-this issue). The offscraped trench sediments form locally build into massive chemoherm complexes (Bohrmann et al., margin-parallel ridges and basins on the lower slope and the same 1998; Greinert et al., 2001). Methane seeps occur globally and style of deformation and topography continues across the upper slope represent a substantial component of the carbon and methane cycles; and coastal ranges. This upper deforming margin is not formed by the material turn-over may be of similar importance to that at the offscraped trench sediments but by a “deforming backstop” of late hydrothermal vent systems of mid-ocean ridges. Nevertheless, Cretaceous and Palaeogene passive margin sediments that predate relatively little is yet known about the ecological variability and subduction (Lewis and Pettinga, 1993). The boundary between lifespans of seeps, about the variability in fluid-flow activity in space offscraped sediments and deforming backstop was inferred to be and time and about their overall impact on the global carbon cycle and significant in defining the location of many of the previously reported hence on climate. For a better understanding of the nature of cold fluid cold seep sites (Lewis and Marshall, 1996). seepage and associated gas hydrates it is necessary to study these New research described by Barnes et al. (2009-this issue)) phenomena in different tectonic and biological environments considerably redefines the boundary between the deforming backstop globally. and frontally accreted sediment, and sheds new light on how this While cold seep systems have already been documented at many boundary influences the location of cold seep sites. The frontally places in the northern hemisphere (e.g., North Sea, Baltic Sea, Black accreted trench sediments, the deforming backstop and back-tilting Sea, North Atlantic, Gulf of Mexico, NW Pacific, Indian Ocean; Judd and cover beds in slope-parallel basins (Lewis, 1980), together form an Hovland, 2007; Suess, 2010), detailed investigations in the SW Pacific actively imbricating frontal wedge that is up to 150 km wide. They are region are still sparse. Indications of methane seepage have been deforming, with increasing dextral strike-slip motion as they reported from around New Zealand, being particularly numerous approach the backstop of Mesozoic “greywacke” meta-sediments along the subduction margin off eastern North Island's Hikurangi that form the main axial ranges of North Island (Walcott, 1978; Barnes Margin (Lewis and Marshall, 1996). Fossil and modern seeps have also et al., 1998). been widely documented on the adjacent land (Campbell et al., 2008). The nature and width of the Hikurangi frontal wedge varies However, despite the Hikurangi Margin appearing to be an ideal considerably along the margin, largely due to changes in plate location for a detailed multi-facetted study of seepage processes, no boundary processes, which include a major northward increase in such study had been proposed for nearly a decade after Lewis and both the velocity of convergence and number of seamounts on the Marshall's (1996) original paper. subducting plate, with a corresponding southward increase in To start closing this knowledge gap, a number of independent but obliquity of convergence and thickness of trench sediments (Lewis closely linked research cruises took place in 2006 and 2007. They were and Pettinga, 1993; Collot et al., 1996; Lewis et al., 1998; Henrys et al., organized and conducted by the Institute of Geology and Nuclear 2006; Barnes et al., 2009-this issue). At the northern end of the Sciences (GNS Science; Lower Hutt, New Zealand), the National margin, the thin trench-fill and rapid subduction of numerous Institute for Water and Atmospheric Research (NIWA; Wellington, seamounts results in little or no frontal accretion and tectonic erosion New Zealand) and the Leibniz Institute of Marine Sciences (IFM- of a steep margin (Collot et al., 1996). The majority of the historical GEOMAR, Kiel, Germany) using the New Zealand research vessel RV seep sites (Lewis and Marshall, 1996) as well as the newly discovered TANGAROA (Cruises TAN0607, TAN0608, TAN0612, TAN0616, and ones discussed here occur in the central zone of slower convergence TAN0711) and the German RV SONNE (Cruise SO191). In this paper with few seamounts, thick trench sediments and gently tapering, we give an overview of three cruises (TAN0607, TAN0616, and SO191) classic frontal accretion. and their interrelated scientific programs. We introduce six seep areas Townend (1997) estimated that more than 20 m3 of fluids are with different biological and geological environments and summarise being squeezed from accreted and subducted sediments along each information that is the context of the various more specialized papers meter of the Hikurangi Margin every year, which results in abundant in this Special Issue. Furthermore we give evidences of individual seep evidence of escaping gas both offshore (Faure et al., this issue; Naudts sites and seep activity that are not presented elsewhere. et al., this issue; Linke et al., this issue) and onshore (Campbell et al., 2008; Nyman et al., this issue). Small seeps of light hydrocarbons are 1.2. Background to seep studies at the Hikurangi Margin widespread on the adjacent land (Kvenvolden and Pettinga, 1989). Fossil submarine seep-carbonates up to 10 m thick and 200 m across, The Hikurangi Margin is at the southern end of the 1000 km long with preserved methane signatures, chemoautotrophic palaeocom- Tonga-Kermadec-Hikurangi subduction systems, where the Pacific munities and near-seabed plumbing systems occur in Miocene Plate subducts increasing obliquely towards the south beneath the bathyal mudstones that outcrop in the coastal hills (Campbell et al., Indo-Australian Plate (Fig. 1). At the southern end of the Hikurangi 2008). In addition, mud “volcanoes” have erupted “spectacularly” Margin, the plate boundary through New Zealand continues as a onshore (Ridd, 1970) and, on the continental shelf, pockmarks have dextral intra-continental transform system to link with an almost been interpreted as evidence of gas expulsion (Nelson and Healy, mirror-image subduction system, where the Indo-Australian crust is 1984). Further seaward, bottom simulating reflectors (BSR), generally subducted beneath the Pacific Plate southwest of South Island inferred to indicate free gas beneath gas-hydrate infused sediment, (Walcott, 1978). Rates of convergence along the Hikurangi Margin occur extensively on the mid and lower slope (Katz, 1981; Townend, range from 45 mm/a at the northern end off East Cape to about 1997; Henrys et al., 2003; Pecher et al., 2004) with the signal of the 38 mm/a at the southern end near Kaikoura, although rotation of the BSR being strongest where geological structures favour fluid migra- forearc increases the rate of convergence to 54 mm/a at the slope-toe tion such as anticlines, layer outcrops and fault systems (Pecher and off East Cape with obliquity of about 40° (Collot et al., 2001). The Henrys, 2003). subducting oceanic plate is the anomalously shallow, 12–15 km thick Slide scars are widespread on all scales along the offshore Hikurangi Plateau (Davy, 1992; Wood and Davy, 1994), consisting of Hikurangi Margin and at least some slope failures, including the ocean crust being covered by turbidites up to 5 km thick. Subduction giant Ruatoria Avalanche deposit, have been partly attributed to

J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx 3

Fig. 1. Currents and tectonic features around New Zealand's North Island and the position of the Hikurangi Margin at the east coast stretching from East Cape (EC) to Cape Palliser (CP). Black arrows and lines are tectonic features as the subduction zone or faults on land. White arrows are water currents (EAUC: East Auckland Current; WE: Wairarapa Eddy; WCC: Wairarapa Coastal Current; DUC: D'Urville Current; SC: Southland Current; ECC: East Cape Current). Wellington (W), Napier (N) and Auckland (A) are shown as well. overpressuring by free gas and loss of strength, perhaps following East Cape Current, record mean speeds ranging from about 6 cm/s off changes in hydrate stability (Barnes and Lewis, 1991; Collot et al., East Cape to 9 cm/s off Wairarapa, but with variability almost the 1996, 2001; Lewis et al., 1998; Pecher et al., 2005; Faure et al., 2006). same as the mean (Chiswell, pers. comm.). South of Hawke Bay, the In addition, erosion of the seabed by “frost heaving” may occur in an main flow of the East Cape Current is more than 80 km from the coast. upper slope zone of intermittent stability where near seabed hydrates Landward, above the outer shelf and upper slope, the relatively cool may form and disintegrate in response to changes in bottom water Wairarapa Coastal Current flows northwards, inshore from the temperature (Pecher et al., 2005). Along the southern Hikurangi southward flow of the East Cape Current (Chiswell, 2002, 2003). Margin, the seaward faces of many slope ridges are incised by Both currents are likely to be highly variable with entrained eddies regularly spaced canyons that could not have been eroded by land- and the effects of tides and internal waves. They interact in a zone derived sediment (Lewis and Pantin, 2002); such “headless” canyons above 2000 m water depth producing variable flows in the vicinity of having been attributed to seeping fluids along several accretionary most of the seep sites. These changing currents are in accord with the margins (Orange and Breen, 1992). At the base of the slope, high degree of current variability found in the studies of seep-fluid anomalous reflectivity and backscatter of some slope-toe thrusts has release by Faure et al. (this issue), Law et al. (this issue)., and Linke et been tentatively attributed also to fluid expulsion (Lewis et al., 1998). al. (this issue).

1.3. Water currents on the Hikurangi Margin 1.4. Bathymetric and seismic coverage pre-2006

Movement of the water above seep sites must be considered in In a very few places, the best bathymetric data available are still studies of the dispersal of vented fluids and of any dislodged solids. based on soundings collected for navigation purposes and as a by- The main oceanic flow along the Hikurangi Margin is the relatively product of science programs (Baldwin and Lewis, 1991). However, in warm and saline East Cape Current (Fig. 1), which flows southwards December 1993, large parts of the margin were surveyed by the sub-parallel to the coast from East Cape to the Chatham Rise where it French RV L'ATALANTE using a SIMRAD EM12 dual swath mapping turns eastwards (Chiswell, 2002). Drifters at 1000 m depth within the system as part of the French — New Zealand GeoDyNZ study of plate

4 J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx

Fig. 2. Bathymetric map based on data recorded during TAN0607, TAN0616 and SO191. Indicated are the six working areas of which zoomed in maps are presented below. The position of those seep sites not presented in the maps of the different working areas are indicated as white dots. The contour lines outside the gray shaded bathymetry are based on a data set supplied by NIWA.

boundary processes (Collot et al., 1996). This dataset produced totally 1.5. Seep-related studies prior to 2006 new images of the margin (e.g. Lewis et al., 1999, 1997; Barnes et al., 1999), as well as a new understanding of many plate boundary Around New Zealand, cold seeps were originally inferred to occur at processes (Barnes et al., 1998). Some areas not covered by the only 13 locations, with the majority along the active Hikurangi Margin, L'ATALANTE survey were mapped using the lower resolution of the including 7 off eastern North Island and 3 off northeastern South Island Hawaii MR1 side-scan sonar system and incorporated into the (Lewis, 1990; Lewis and Marshall, 1996; Orpin, 1997). Fig. 2 shows the GeodyNZ results. Since the late 1990s, some localized areas have location of these northern seep sites (e.g. LM-1 or LM-9), where the been mapped in much higher resolution with the SIMRAD EM300 number originates from the number given by Lewis and Marshall multibeam system (30 kHz) mounted on RV TANGAROA. As new data (1996).Thissitenumbering,prefixed by LM, is used throughout the are obtained, digital maps of the margin are continually updated by Special Issue. NIWA. Some of the sites had been located first by fishermen, who Seismic reflection coverage of the Hikurangi Margin is variable recovered unusual clams orcarbonate,orobservedflares in having been collected for a wide variety of scientific and industry echograms, some were based on carbonate chimneys found by ROV projects over nearly half a century. However the data set is sufficient surveys, and some were the result of targeted dredge and sounder to give a good idea of the margin's structure (Barnes et al., 2009-this surveys of known and potential seep sites in 1991 and 1994 (NIWA issue) and provide the background for the detailed surveys of each of cruises 2044 and 3017). Indications for seepage in the form of flares the working areas described in this Special Issue (Crutchley et al., on Opouawe Bank were identified by NIWA fisheries scientists in 1996 2009-this issue;Pecher et al., this issue); Schwalenberg et al., this (L. Carter, pers. comm.; Law et al., this issue). The only live specimen issue-a,b;Krabbenhöft et al. (this issue); and Netzeband et al., this of mollusc fauna recovered from the seep locations identified by Lewis issue). and Marshall (1996) was later described as a new species,

Fig. 3. Bathymetric and backscatter map of the Opouawe Bank area just offshore Cape Palliser. A total of 13 seep sites have been identiﬁed. Four of them (Matata, Tete, Popango and Takapu) have not been visually conﬁrmed but sidescan (Klaucke et al., this issue), bathymetric and backscatter data (image B) give strong indications that these locations are also seep sits.

J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx 5

6 J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx

Fig. 4. Echograms showing flares at Builder's Pencil recorded at the same time by the different systems and frequencies available during RV TANGAROA cruises. The two flares on each echogram show the same flare crossed twice during the time the ship sailed a loop over the site (Fig. 12). During the left flare was recorded the ship was about 100 m to the west of the actual seep site (see Fig. 12B). The horizontal dashed line represents the phase boundary for pure methane hydrate at ambient salinity and temperature conditions.

Bathymodiolus tangaroa (von Cosal and Marshall, 2003), inferred to be described in much more detail by Nyman et al. (this issue) while endemic to New Zealand seeps. Isotopic analysis confirmed that the Campbell et al. (this issue) and Liebetrau et al. (this issue) describe supposed seep carbonates recovered from the Hikurangi Margin are those found offshore. methane-derived (δ13C −39‰ PDB; Lewis and Marshall, 1996), however the carbonates from offshore Otago Peninsula, south of the 2. Methods Hikurangi Margin, were interpreted to have formed around freshwater springs in shallow coastal water as a result of mixing with sea The conducted seep and gas hydrate research along the Hikurangi water (Orpin, 1997). Margin used state-of-the-art systems, techniques and methods In 2004, the opportunity was taken to conduct a 24 h multibeam related to geophysics, hydroacoustics, video-mapping, geochemistry, bathymetric survey and water column studies for methane analyses at biology and microbiology as well as geology (see Appendix A). Rock Garden using RV TANGAROA. This small survey gave the first Finding active and/or fossil seeps at the seafloor proved to be the most high resolution view of the seafloor morphology and also found new crucial part of seep exploration. Morphological indications such as hydroacoustic and geochemical indications of methane bubble release knolls, small hills (i.e. chemoherms), mud volcanoes and pockmarks at the southern edge of Rock Gardens plateau-like top (Faure et al., are often associated with well developed seep sites (see Judd and 2006). Hovland, 2007 and references therein). Linking them to backscatter In February 2005, NIWA began a time-series study at two seep information from multibeam and/or sidescan surveys often reveals sites now called North and South Tower on the Opouawe Bank (Fig. 3). increased backscatter due to carbonate and/or gas hydrate cementa- The study primarily aimed at quantifying methane emissions to the tion or free gas just underneath the seabed. If free gas is released in the water column and across the air-sea interface. The South Tower flare water column (bubbling seep) it can be detected, mapped and traced was a constant feature over the three year survey, in both position and back to the actual bubble vent at the seafloor by using hydroacoustic magnitude, with methane emissions primarily constrained to bottom methods, singlebeam echosounders or sidescan sonar systems. waters (Law et al., this issue). In addition to offshore sites, fossil onshore seep sites have been 2.1. Multibeam mapping identified and studied before 2006 and since, with two different types of carbonates found (Campbell, 2006; Campbell et al., 2008; Nyman et Multibeam data presented here (Fig. 2) and in other papers of this al., this issue). Some carbonate is methane derived and formed at the issue have been recorded with the EM300 (30 kHz, 2 by 2 degrees, seafloor surface; it is composed of aragonite and calcite-cemented 135 beams) onboard RV TANGAROA (TAN 0607 and TAN0616) and sediments with incorporated chemoautotrophic fauna. Other carbo- the EM120 systems (12 kHz, 2 by 2°, 191 beams) onboard RV SONNE nates are calcitic to dolomitic, forming pipe, chimney and doughnut (SO191). Various sound velocity pro files were recorded during the shaped rocks of centimeter to few meters in diameter and length; they cruises and were applied during data processing. The ship's speed was most likely represent the plumbing system for upward migrating usually between 4 and 8 knots, or 2–3 knots when combined with fluids. Campbell (2006) and Campbell et al. (2008) give a first sidescan sonar surveys (SO191). overview of the fossil seep sites onshore New Zealand, describing sites Processing was done using the open source software package MB with petrographic and isotopic characteristics very similar to those System (5.7.1) which used sound velocity profiles acquired by CTD to seen offshore. These onshore plumbing system carbonates are now export geo-referenced x (longitude), y (latitude) and z (water depth)

J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx 7

Table 1 Location and general description of seeps along the eastern coast of New Zealand's North Island. All sites except those named LM-xx (from Lewis and Marshall, 1996) were discovered in 2006-2007 or were for the ﬁrst time studied in more detailed. Some seep sites are listed with more than one location, this is because of more than one isolated occurrence of seepage in close proximity. Coordinates are given in degree and decimal minutes (dd:mm.mm). MB: multibeam; BS: backscatter of multibeam. The numbers in the “Remarks” column refer to Table 2.

# Seep name Latitude S Longitude E Depth m Remarks (evidence in #/)

Ritchie Ridge 1 LM-1 39:24.993 178:24.268 1130 Carbonates and clam shells sampled (12) 2 Builder's-Pencil 39:32.636 178:19.944 797 Carbonates, clam shells and tube worms observed and sampled; ﬂare (2, 23, here)

Omakere Ridge 3 LM-9 40:01.089 177:51.616 1150 Carbonates, clam shells and tube worms observed and sampled; ﬂare; evidence from sidescan, MB and BS (2, 6, 7, 23, here) 40:00.999 177:51.769 1151 40:00.603 177:52.358 1160 4 Kakapo 40:02.141 177:48.400 1167 Carbonates, clam shells and tube worms from observations; evidence from sidescan, MB and BS, seismic (7, here) 5 Kaka 40:02.140 177:47.937 1168 Carbonates, clam shells and tube worms from observations and sampled; evidence from sidescan, MB and BS, seismic (7, 15, 23, here) 6 Kea 40:02.240 177:47.714 1168 Carbonates, clam shells and tube worms from observations and sampled; evidence from sidescan, MB and BS, seismic (7, 15, 23, here) 7 Bear's-Paw 40:03.187 177:49.252 1100 Carbonates, clam shells and tube worms from observations and sampled;evidence from sidescan, MB and BS, seismic; high water column methane conc;gas hydrate recovered (7, 15, 23, here) 8 Moa 40:03.235 177:48.802 1118 Carbonates and corals from observations and sampling (fossil seep site) (6, 7, 13, here)

Rock Garden 9 LM-3 39:58.401 178:13.837 863 Flare; seismic evidence (LM-3A) (4, here) 39:58.607 178:14.221 919 Carbonates, clam shells and tube worms from observations and sampled; living Bathymodiolus; flare; evidence from sidescan, MB and BS (4, 6, 15, 16, 23, here) 40:00.286 178:11.905 635 Carbonates, clam shells and tube worms from observations; seismic evidence (Weka A), (4, here) 10 Weka 40:00.205 178:12.058 655 Carbonates, clam shells and tube worms from observations; seismic evidence (Weka B), (4, here) 40:00.022 178:12.245 715 Carbonates, clam shells and tube worms from observations; seismic evidence (Weka C), (4, here) 40:01.936 178:09.693 660 Carbonates, clam shells from observations and sampled; flare; seismic evidence; high water column methane conc. (7, 15, 23, here) 11 Faure Site 40:01.960 178:09.401 654 Carbonates, clam shells from observations; flare (Faure A) (4, 6, 14, 16, 22, here) 40:01.498 178:9.876 641 Flare; seismic evidence (BSR pinch out, gas) (Faure B) (4) 12 RG-Knoll 40:02.379 178:08.599 767 Carbonates, clam shells and bacteria mats from observations and sampled; evidence from MB (2, 4, 23) 13 Kakariki 40:04.900 178:11.400 790 Flare in sidescan; evidence from MB (14, here)

Uruti Ridge 14 LM-10 41:17.470 176:33.017 729 Carbonates, clam shells, tube worms and bacteria mats from observations and sampled; flare; evidence from MB (2, 23, here) 15 Tomtit 41:17.446 176:33.187 729 Carbonates, clam shells, tube worms and bacteria mats from observations and sampled; evidence from MB (LM-10 East) (2, 23, here) 16 Kereru 41:17.161 176:35.469 727 Carbonates, clam shells, tube worms and bacteria mats from observations and sampled; flare; evidence from MB (2, here) 17 Hihi 41:17.687 176:33.548 744 Carbonates, clam shells, tube worms and bacteria mats from observations and sampled; flare; evidence from MB (2, 23, here)

Opouawe Bank (Wairarpa) 18 Tui 41:43.288 175:27.091 815 Carbonates, clam shells, tube worms and bacteria mats from observations; flare; evidence from sidescan, MB, BS and seismic (8, 9, 11, 17, here) 19 Tuatara 41:43.239 175:26.558 827 Rocks (carbonates?) from observations; evidence from sidescan, MB and BS(8, here) 20 Takahe 41:46.368 175:25.651 1058 Bacteria mats from observations and sampling; Flare; gas hydrate sampled; evidence from sidescan, MB, BS and seismic (8, 15, 17, 20, 23, here) 21 North-Tower 41:46.911 175:24.083 1052 Carbonates, clam shells, tube worms and bacteria mats from observations and sampled; flare; evidence from sidescan, MB, BS and seismic (2, 8, 9, 11, 15, 17, 20, 22, 23, here) 22 South-Tower 41:47.300 175:24.521 1056 Carbonates, clam shells, tube worms and bacteria mats from observations and sampled; flare; gas hydrate sampled; evidence from sidescan, MB, BS and seismic (2, 8, 9, 11, 17, 20, 23, here) 23 Riroriro 41:47.360 175:22.754 1084 Carbonates, clam shells, tube worms and bacteria mats from observations; flare; evidence from sidescan, MB, BS and seismic (8, 17, here) 24 Pukeko 41:47.153 175:23.465 1060 Carbonates, clam shells, tube worms and bacteria mats from observations; evidence from sidescan, MB, BS and seismic (8, 17) 25 Piwakawaka 41:47.664 175:22.348 1095 Carbonates, clam shells, tube worms and bacteria mats from observations; living Bathymodiolus; evidence from sidescan, MB, BS and seismic (8, 17, here) 26 Tieke 41:43.639 175:26.983 851 Boulders and outcropping rocks from visual observations; evidence from sidescan, MB, BS and seismic (8, 17, here) 27 Takapu 41:46.750 175:26.245 1086 Evidence from sidescan, BS (8, here) 28 Tete 41:44.531 175:27.214 972 Evidence from sidescan, MB and BS (8, here) 29 Papango 41:45.704 175:27.267 1065 Evidence from MB, BS and seismic (17, here) 30 Matata 41:44.567 175:25.407 957 Evidence from MB BS (here) 31 Pahaua 41:41.830 175:41.220 1465 Flare; higher methane concentrations (11) 32 Seep B 41:45.035 175:25.949 1005 Seismic evidence (17) ? Ruru (?) 41:51.232 175:15.426 1631 Questionable flare (here)

Others 33 Miromiro 41:45.171 175:07.291 860 Flare (here) 34 LM-4 41:30.0 174:52.0 100 Carbonate chimneys, bivalve shells (12) 35 LM-5 41:50.0 174:26.0 128 Bivalve shells carbonate cemented (12) 36 LM-11 41:27.0 174:47.0 250 Carbonate chimneys (12)

8 J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx

Fig. 5. Echograms of flares at Opouawe Bank, recorded during TAN0616 (EA60, 38 kHz). Image A shows the backscatter of bubbles released from the Takahe site and two time the much larger flare at South Tower that was crossed in two opposite directions. Image B shows the twin-shaped North Tower flare which point to at least two bubble release areas at the seafloor. The x-axes are time axes, the y-axes give water depth in meter. data. These xyz data were edited with Fledermaus 6.7 (by IVS-3D) and also used for echogram visualization in this and other papers of this plotted with GMT (4.2) using near-neighbour or surface as gridding Special Issue (e.g. Crutchley et al., 2009-this issue; Jones et al., this issue); algorithm. Depending on the size of the displayed area, the grid estimates of flare dimensions being used to quantify methane emission spacing varies between 150 m and 10 m. All maps shown throughout rates in Law et al. (this issue). this issue are in Mercator projections with WGS84 as reference Care must be taken in interpreting echograms. Fig. 4 shows an ellipsoid. Backscatter processing was carried out with the beta version example of how different frequencies and systems register the bubble of FMGeocoder that was kindly provided by IVS-3D. induced backscatter in the water column. The most advanced/ sensitive system used was the ES60 (38 kHz); it shows the highest 2.2. Hydroacoustic bubble detection/flare imaging resolution and highest flare in comparison to the simultaneously used EK500. The echogram of the 27 kHz channel of the EK500 27 kHz Hydroacoustic detection of water column plumes emanating from system showed similar results as the ES60 although with less the seafloor is a first order remote proof of active fluid seepage at any resolution due to the lower sampling rate of the received signal. site. Hydroacoustic detection by singlebeam echosounders has provided Very different are those data from the EK500 12 kHz that show the an efficient method for more than 20 years and has been discussed in flare much wider and significantly lower. many publications dealing with seepage and methane fluxes (Mer- This comparison reveals that different frequencies and systems are ewether et al., 1985; Hornafius et al., 1999; Greinert et al., 2006, Naudts generally able to detect the bubble source at the seafloor more or less et al., 2006; Artemov et al., 2007, Ostrovsky et al., 2008; Sauter et al., well, but assumptions about rising height and thus bubble dissolution 2006; Schneider et al., 2007). The basic principle for detecting bubbles depths have to be looked at more carefully and in detail. This is with an echosounder is the strong backscattering of the transmitted particularly important when trying to link the flare height with e.g. pressure wave at the impedance contrasts between water and gas the gas hydrate phase boundary. The termination of the flare for the bubbles. This creates flare-shaped backscatter features in echograms, 12 kHz data coincides with gas hydrate phase boundary at 660 m which is the reason why the respective surveys are called flare-imaging water depth (using the CSMHYD program of Sloan, 1998) in ambient surveys and the locations of such features are called flare positions salinity and temperature conditions (34.5 psu; 7.89 °C). But the two (Egorov et al., 1998; Greinert et al., 2006). Due to the increasing footprint other frequencies undoubtable show that bubbles rise for at least of the acoustic lobe with increasing depth, it is not always possible to another 100 m outside the gas hydrate stability zone. give exact locations of the actual bubble releasing spot at the seafloor (Nikolovska et al., 2008). Thus, flare-imaging based on singlebeam 2.3. Visual seafloor observations and ground-truthing echosounder data cannot resolve bubble vents that are only meters apart. Here visual observation is required in addition. Visual observations by towed camera vehicles and ROV (DTIS, OFOS, During TAN0607, TAN0608, TAN0612, TAN0616, and TAN0711 the and ROV ‘GENESIS’) utilized the hydroacoustic underwater navigation two echosounder systems onboard RV TANGAROA the EK500 using 27 system of both research vessels (GAPS or POSIDONIA on RV SONNE; HPR and 12 kHz and the ES60 using 38 kHz were recorded continuously with on RV TANGAROA). These systems were connected with the OFOP the Echolog 500 (Myriax) and ER60 (Simrad) recording software, software package (Hütten and Greinert, 2008) for navigation and real- respectively. Flare positions were logged as soon as indications were time logging of observations. With OFOP, video and photo footage could seen live on the echogram screen. The positions of the flare-roots were be easily geo-referenced and used for ground-truthing and mapping of refined after reviewing the data in Echoview (Myriax). Echoview was various seep habitats. Sediment and benthic sampling using TV-guided

J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx 9

Fig. 6. Compilation of echograms from various seep sites at the Hikurangi Margin. The change in rise angle of the Tui flare (D) is not caused by a change in ships speed (which was continuously about 2.1 m/s) but due to a significant change of strong horizontal bottom water currents to much lower velocities at 700 m water depth. By the far the tallest flare would be Ruru (G), but the poor quality of the data and high ship speed during transit do not allow to identify Ruru as a bubble cause flare, undoubtedly. The x-axes of all echograms are time axes, the y-axes give water depth in meter. All echograms have the same y-axis scale.

10 J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx multi-corer, gravity-corer, grab, and epibenthic sleds recovered material The Tieke site is inferred from a clear sidescan anomaly (Klaucke et that was use for more detailed studies of the different habitats. al., this issue) corresponding with a marked morphological rise 700 m south of Tui. It forms a kind of nose standing out from the hill flank. Multibeam backscatter data indicate that the area between Tui and 3. Results Tieke consists of a hard surface either due to outcropping bedrock and/or strong (methane-derived) cementation (Fig. 3). Klaucke et al. Combining the results of all cruises (see Appendix A), and (this issue) suggest two other seeps, Tete and Takapu, based on including the previously known seep locations defined by Lewis and sidescan observations. High multibeam backscatter and a weak but Marshall (1996), a total of 36 seep sites have now been identified on distinctively positive morphological expression (3 m high and 500 m the Hikurangi Margin with 32 of them being discovered during 2006 by 250 m in size) at Tete (Fig. 8) and higher backscatter in multibeam and 2007. Of these 32, 25 were confirmed by visual observations data at both sites support their assumption (Fig. 3). and/or sampling of the seabed (Table 1, Fig. 2). The seeps are West of Takahe, where gas hydrates were recovered, lie North concentrated in six main areas (Fig. 2); all are on top or along Tower, a large, rocky seep site showing a strong and persistent flare; morphological features in a range from 635 to 1465 m water depth. Pukeko and Riroriro characterized as smaller chemoherm sites; and Because most of the following papers concentrate on one or two of finally Piwakawaka on top of an east-west running fault line (Fig. 3; the six areas, we outline the results for each area from Opouawe Law et al., this issue). Near surface gas hydrate cored during SO191 at Bank in the south to Builder's Pencil at Ritchie Ridge in the north. Takahe (Schwalenberg et al., this issue b) occurred as veins of mm to Because of the large number of new seeps discovered during the cm thickness at 2.4 m sediment depth. In addition, a fist-sized solid cruises, sites were given informal names. Most of those re-visited or chunk of gas hydrate was dredged by a benthic sled during TAN0616 discovered during SO191 were named after native New Zealand at South Tower. Unfortunately, no geochemical sample could be taken birds in the Māori language (http://www.nzbirds.com/), while from this piece of hydrate as it fizzed away too rapidly. others kept their descriptive name given during TAN0616 or The most intensely studied seeps on Opouawe Bank are North Tower SO191. North Tower, South Tower and Builder's Pencil owe their and Tui. Faure et al. (this issue) describe methane release into the water names to the shape and height of their flares (Figs. 4 and 5). Bear's column above both sites and demonstrate the spreading of methane rich Paw was named for its shape in sidescan data as can be seen in water towards the SW for over 20 km along a specificdensitylayer.Law Fig. 9ainJones et al. (this issue). et al. (this issue) give a very detailed description of the currents and the influence of density on the methane distribution once it enters the water 3.1. Opouawe Bank (Wairarapa) column as free or dissolved gas. Repeated crossing of South and North Tower in successive cruises proved that the bubble release here has been The southernmost study area is only 16 km offshore from the consistently active since at least 2005 (although earliest records date southern tip of New Zealand's North Island, and the remote back to 1996). The occurrence of faunal assemblages of clams, tube Wairarapa coast (Fig. 2). It is the most studied area, both temporally worms, and a high densities of ampharetid polychaetes (Baco et al., this and spatially (Law et al., this issue; Faure et al., this issue). The ENE- issue Sommer et al., this issue; Thurber et al., this issue make North and striking, 16 km long kidney-shaped Opouawe Bank has a northern South Tower two of the most biologically diverse seeps along the hill that rises up to 815 m water depth (Fig. 3). In total, 14 seep sites Hikurangi Margin. The occurrence of massive carbonates at both sites have now been identified on the bank by visual examination, suggests that seepage has persisted for a considerable time. sampling, flare detection or inference from morphological and Presented here are observations from the last OFOS track during multibeam backscatter data or seismic data. No indications of SO191 (#292-OFOS-22) that studied Piwakaka, the western most seepage had been found prior to 2005 in this area, mainly because of seep site on Opouawe Bank. The video and photo footage revealed a the limited research there. Although not on the bank, the Pahaua complex of scattered chemoherm blocks with living tubeworms and site, about 25 km to the ENE of Opouawe Bank, is in the vicinity few clam shells. Surrounding those blocks occur scattered patches of (Table 1). At 1465 m water depth, this seep, discovered due to the white mats of the genus Beggiatoa as well as dark gray beds of observation of a flare (Law et al., this issue), is the deepest along the ampharetid polychaete sites (‘rain drop sites’, Sommer et al., this Hikurangi Margin so far. issue; Fig. 7). In addition one patch of living mussels of the genus The Tui seep is located directly on top of the northern hill of Bathymodiolus was seen (Fig. 7J). No bubbles were observed visually Opouawe Bank. Tuatara, 750 m to the west, forms a pronounced or hydroacoustically but nevertheless this site is actively releasing 12 m high knoll with a diameter of 200 m. Tui and another seep, fluid. Takahe, were discovered by flare-imaging surveys during TAN0616, Two more seeps, Matata and Papango, have been inferred from thesamecruisealsoconfirmed hydroacoustically the activity of the increased multibeam backscatter response at low but positive morpho- North and South Tower site (Figs. 5 and 6). Whereas Tui showed logical expressions (Fig. 8). As with Tete and Takapu, these two sites evidence of considerable present activity in the form of high were not studied in more detail and the visual proof of seep features still methane concentrations in the water column (Faure et al., this has to be undertaken. In contrast seepage is likely at Papango as it lies at issue), flares, chemoherm structures, and abundant live chemoau- the eastern most end of a line of five other well studied seeps totrophic fauna (Fig. 7), visual examinations of Tuatara showed only (Piwakawaka to Takahe), and probably also overlies the E–Wstriking a very few boulders of possibly methane-derived carbonates that fault that cross the entire Opouawe Bank and outcrops at North Tower suggest an old, not presently active seep. The strong backscatter (Law et al., this issue). In addition Netzeband et al. (this issue) reports seen in sidescan (Klaucke et al., this issue) and multibeam data seismic anomalies beneath Papango that indicate fluid (gas) migration. (Fig. 3) provide evidence that the seafloor cementation area is much Finally a flare was identified at another site, Miromiro at 860 m water larger than the morphological expression, pointing towards a depth, west of Opouawe Bank in the Cook Strait when transiting during formerly very active seep history for Tuatara. TAN0616 to Opouawe Bank (Fig. 6).

Fig. 7. Seafloor images from different seeps in different areas as indicated. Strong carbonate cementation of the seafloor (with cracks and fissures that allow fluids to migrate upward and tube worms (A to D, F, G, and I) as well as clams (A to I) to live are a common feature at all sites. The extreme dense and widespread coverage of the seafloor with shells at Builder's Pencil was unique for the study area. Mainly scattered chemoherm-type carbonate blocks have occurred at the deeper sites at Opouawe Bank. Living mussels of the genus Bathymodiolus could be identified (J, lower left corner) at Piwakawaka, here, “rain drop site” patches with sharp edges towards normal, strongly bioturbated sediment occur widely distributed (K). Image L is taken in a pockmark at Ritchie Ridge with no signs of active seepage, but corals commonly settling on blocks in the centre of these pockmarks.

J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx 11

12 J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx

Fig. 8. Bathymetric evidence of seep structures from Matata and Tete (both Opouawe bank) as well as Kakariki from Rock Garden. The up to several meters high structures indicate massive carbonate cementation as seen e.g. at Piwakawaka or Bear's Paw.

3.2. Uruti Ridge during TAN0607 yielded elevated methane concentrations of up to 14 nM close to the bottom (Faure et al., this issue), confirming that Seepage from LM-10 on Uruti Ridge (Fig. 9) was described by Lewis they are caused by methane bubbles. This maximum concentration is and Marshall (1996) as “astronglyreflective plume coming from 725 m not high compared to other measurements made during SO191 (Faure water depth”. This site was revisited during TAN0607 and TAN0616 and et al., this issue) and may indicate that sampling missed the centre of both times a strong flare was detected. Visual observations with the DTIS the flare source. system (TAN0616) showed that three peaks on top of the westernmost hill at Uruti Ridge are caused by massive carbonate cementation that led 3.3. Porangahau Ridge to the formation of knolls up to 50 m high (Liebetrau et al., this issue). From west to east these are LM-10, Tomtit, and Hihi. Another knoll- Porangahau Ridge is much deeper (1950 m to 2400 m) than the forming seep, Kereru, lies on the adjacent hill to the east (Fig. 9). All other studied areas. The reason for studying Porangahau Ridge was a seeps were visually investigated and sampled for biological studies very strong BSR underlying an anticlinal structure, suggesting the during TAN0616 (Baco et al., this issue). The seep assemblages at all four possibility of free gas accumulation and transport along conduits seeps investigated at Uruti Ridge consisted of tube worms and clams in with release of methane from seep sites at the seafloor. Seismic fissures and cracks in an almost completely cemented seafloor (Fig. 7; studies (Pecher et al., this issue), sediment coring and heatflow also Baco et al., this issue; Liebetrau et al., this issue). LM-10 was also measurements (Schwalenberg et al., this issue a) were undertaken sampled during SO191 and massive methane-derived carbonates were during TAN0607, together with three CTD casts. Methane concen- recovered (Liebetrau et al., this issue). trations from water sampled during the CTD casts all show only Presented here are flares that were observed during TAN0616 at background concentrations that do not reach more than 2 nM below LM-10, Hihi and Kereru (Fig. 6). Water sampling casts on these flares 1000 m water depth and only increase towards the sea surface to

J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx 13

Fig. 9. Bathymetric map of Uruti Ridge showing the four visited seeps sites. All of them build knolls of massive carbonate of up to 50 m height.

become slightly oversaturated with respect to the atmosphere Sidescan surveys during SO191 revealed five more seep sites, all of (4.4 nM; Faure, pers. comm.). During SO191, an additional CSEM them about 5.5 km towards the SW of LM-9 (Fig. 10). Detailed profile was recorded (Schwalenberg et al., this issue a) but no other descriptions of sidescan, sub-bottom and visual observations of these attempts (e.g. visual or sidescan surveys) were undertaken to find sites, named Kaka, Kea, Kakapo in the west and Bear's Paw and Moa seeps in this area. Backscatter analyses of the EM300 data recorded 2.5 km to the SE, are given in Jones et al. (this issue). The faunal during TAN0607 show no clear indications of potential seeps. Only assemblages at all these five sites are similar to those at LM-9, with the at two locations, each approx. 300 m in diameter, we observed exception that the massive carbonates at Moa support abundant cold slightly elevated backscatter after re-processing the data with the water corals suggesting that this is an old and now inactive seep site FMGeocoder software that might indicate a stronger cementation of (Jones et al., this issue; Liebetrau et al., this issue). Bear's Paw the sediment (data not shown). These sites are located on the supported the highest abundances of chemoautotrophic taxa yet landwards side of Porangahau Ridge at 177:31.290 E/40:49.442 S recorded on the Hikurangi Margin, with very high densities of both and 177:32.086 E/40:49.369 S in water depths of 2115 and 2060 m, Lamellibrachia sp. tube worms and Calyptogena sp. clams. respectively. Intense water column work including physical (CTD and mooring) and geochemical studies was performed at and around Bear's Paw 3.4. Omakere Ridge during SO191. High methane concentrations of up to 380 nM were observed with clear isotopic indications that the methane is From Lewis and Marshall (1996), one seep site based on flare biogenically formed (Faure et al., this issue). Work by Linke et al. observation was known from Omakere Ridge (Fig. 10) before (this issue) included ADCP, and high resolution CTD measurements TAN0607 (LM-9). This site was revisited during TAN0607 and undertaken during a FLUFO lander deployment. They discovered that hydroacoustic surveys confirmed a prominent flare at LM-9 a non-tide dependent bubble outburst occurred that created a plume (Fig. 10). The site was subsequently cored for sedimentological due to high concentrations of methane perhaps coupled with higher purposes and to extract possible methane-influenced foraminifera porewater temperatures. Gas hydrate was recovered in a gravity core (unpublished data NIWA, Helen Neil). Martin et al. (this issue) at Bear's Paw in 93, 105 and 125 cm core depth. In Bialas et al. (2007) confirmed this influence on foraminifera in cores taken during it is mentioned that “several” cores recovered gas hydrate at Bear's

SO191. Water column samples showed CH4 concentrations of up to Paw, but no further details are given. 40 nM (Faure et al., this issue). LM-9 was revisited during TAN0616 The detailed multibeam data shown here indicate areas of localized and again showed bubble release. Camera observations and bottom strong backscatter suggest four possible new seep sites (a to d in Fig. 10). trawling revealed a characteristic seep faunal assemblage of tube However, sidescan data recorded during SO191 do not show any worms, clams and bacteria patches (Baco et al., this issue)together anomalies at these places (Jones et al., this issue). This could be due to with irregular and porous carbonates lying isolated or in dense the absence of any morphological expression (no chemoherm or other clusters at the seafloor (Jonesetal.,thisissue). Both sidescan and carbonates laying on the seafloor) or a sediment cementation that is DTIS surveys showed that LM-9 consists of three isolated patches, presently too deep to be detectable by the high frequency system of the two larger ones 300 m apart and a third much smaller one 1.2 km to sidescan (75 kHz) but which can be imaged using the lower frequency the NE (Table 1). At the southern most patch, which corresponds of the EM120 (12 kHz). The existence of additional seeps at these four closely to the original location stated in Lewis and Marshall (1996), locations is speculative but might merit study in the future (a: 40:2.162 flares have been repeatedly observed during TAN0607 and TAN0616 S/177:51.740 E; b: 40:1.914 S/177:52.101 E; c: 40:0.950 S/177:53.175 E; (see Jones et al., this issue). d: 39:59.727 S/177:53.608 E).

14 J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx

Fig. 10. Bathymetric (a) and multibeam backscatter map of Omakere Ridge showing six seep sites that are conﬁrmed by visual investigations. Three sub-locations are given for the LM-9 site as the two southern once are almost linked to each other and the northern one only consist of a small patch of carbonate as can be seen in sidescan data (Jones et al., this issue). Locations named a, b, and c and d are inferred from high backscatter patches seen in the multibeam data.

J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx 15

Fig. 11. Bathymetric map of Rock Garden showing the studied seep locations. Crutchley et al. (this issue) distinguish between three different sites at Weka (a to c) and gave the name ‘Faure B’ to a BSR outcrop and ﬂare position slightly north of Faure Site.

3.5. Rock Garden reasons for the flat top of the ridge, seafloor erosion by gas hydrate induced frost heave versus the subduction of a seamount. The results One seep location, LM-3 (Fig. 11), on the north-eastern side of from Kukowski et al. (this issue) infer the possibility of large landslides in Rock Garden, was reported by Lewis and Marshall (1996) based on the Rock Garden area. two observations of a flare in 1994 and the dredging of a methane- During TAN0616, a hydroacoustic survey was performed across derived carbonate chimney and clam shells. During TAN0607 the flare LM-3 but bubble release was not detected. Instead a knoll-like at LM-3 (Fig. 6) was observed again and two additional flares at the morphological feature, the “Rock-Garden Knoll”, was studied because southern edge of the Rock Garden plateau were discovered (Pecher et higher backscatter intensities in the water column during flare- al., 2007) at a location where Faure et al. (2006) report a flare and imaging surveys had been detected in the water column. DTIS higher methane concentrations during the TAN0411 cruise in 2004. observations showed a massive occurrence of mainly roundish This area was thus called Faure Site. No flare was observed at LM-3 carbonates but only a single live tube worm as evidence of present during TAN0616. seepage (Baco et al., this issue). The near-by Faure Site was not visited Seismic data suggest gas-filled faults or chimneys feeding Faure Site during TAN0616 but bubble release was detected during the and LM-3 (Crutchley et al., 2009-this issue). The same authors also echosounder survey as a flare (Fig. 6). suggest that another site, Faure B, exists where the BSR pinches out at the Prolonged visual observation, sampling and monitoring was seafloor and a weak flare was detected during TAN0607. Using carried out in the Rock Garden area during SO191. Naudts et al. bathymetric and seismic data from TAN0616 and SO191, Ellis et al. (this issue) used camera (OFOS) and ROV surveys but also video (this issue) and Kukowski et al. (this issue) discuss the most likely footage from TV-guided multicorer and lander deployments to

16 J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx

Fig. 12. Bathymetric map of the Builder's Pencil area 15.5 km south of LM-1. Inset map B shows the loop that was sailed during the time the Builder's Pencil ﬂare was detected twice with the singlebeam echosounder onboard of RV TANGAROA (Fig. 8).

describe the differences of the seep areas around Faure Site and LM-3 gas release at Faure Site yielded ﬂuxes of up to 12.6 mol CH4 per at meter scale. During the observations, bubble release was visually minute (equal to 4.4 l/min at in situ pressure). Linke et al. (this issue) conﬁrmed at LM-3 and Faure Site. Visual estimates by ROV of the free present additional geochemical and acoustical data from lander

J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx 17

Table 2 List of references that present data for one or several of seep sites along the Hikurangi Margin.

# Author Areas Published

1 Barnes et al. Ritchie Ridge, Rock Garden, Omakere Ridge, Uruti Ridge, Opouawe Bank This issue 2 Baco et al. Ritchie Ridge, Rock Garden, Omakere Ridge, Uruti Ridge, Opouawe Bank This issue 3 Campbell et al. Rock Garden, Omakere Ridge, Uruti Ridge, Opouawe Bank This issue 4 Crutchley et al. Rock Garden This issue 5 Ellis et al. Rock Garden This issue 6 Faure et al. Rock Garden, Omakere Ridge, Uruti Ridge, Opouawe Bank This issue 7 Jones et al. Omakere Ridge This issue 8 Klaucke et al. Opouawe Bank This issue 9 Krabbenhoeft et al. Opouawe Bank This issue 10 Kukowski et al. Rock Garden This issue 11 Law et al. Opouawe Bank, Cook Strait This issue 12 Lewis and Marshall Ritchie Ridge, Rock Garden, Omakere Ridge, Uruti Ridge, Cook Strait NZJGG (1996) 13 Liebetrau et al. Rock Garden, Omakere Ridge, Uruti Ridge This issue 14 Linke et al. Omakere Ridge, Rock Garden This issue 15 Martin et al. Rock Garden, Omakere Ridge, Opouawe Bank This issue 16 Naudts et al. Rock Garden This issue 17 Netzeband et al. Opouawe Bank This issue 18 Nyman et al. Onshore seeps only This issue 19 Pecher at al. Porangahau Ridge This issue 20 Schwalenberg et al. a Opouawe Bank This issue 21 Schwalenberg et al. b Porangahau Ridge This issue 22 Sommer et al. Rock Garden, Omakere Ridge, Opouawe Bank This issue 23 Thurber et al. Ritchie Ridge, Rock Garden, Omakere Ridge, Uruti Ridge, Opouawe Bank This issue deployments at Faure Site and show that bubble release is tidally more vigorous in the past and have persisted for a considerable period. influenced. The same authors also report another flare site (Kakariki) During SO191, sidescan sonar and seismic surveys (OBS/H deployments, detected in sidescan data recorded during SO191. This flare is in MCS) of Builder's Pencil and LM-1 showed no evidence of active seepage 790 m water depth, and very close to a 200 m by 120 m wide and (Bialas et al., 2007) so Builder's Pencil is the least studied of all six seep about 2 m high “bump” at the southern flank of Rock Garden (Fig. 8). areas described here. Only described in this study is a seep site that was found during the In contrast to the other five areas investigated, the bathymetric first camera transect of SO191 (#41 OFOS-1), the Weka site. It data here show pockmark-like features around Builder's Pencil that appeared to be widespread and extending for 800 m with three main are up to 600 m wide and 70 m deep. Seafloor observations during clusters of seep indications. At those areas the seafloor had a very hard SO191 (OFOS-20) targeted four adjacent pockmarks north of Builder's substrate, either due to carbonate cementation or outcropping Pencil hoping to find indication of seepage (Fig. 12). The seafloor in bedrock. Clam shells and tube worms were present in fissures and the central parts of each depression consisted of randomly distributed cracks (Fig. 7) and occasionally occurred in meter-wide patches. rocks and boulders exposed at the seafloor or lying half buried. They Although Weka is very large, it is apparently not a currently active show the typical brown Mn/Fe-oxid coating of bottom-water-exposed seep site; flares were not detected during any of the cruises and this rocks. This hard substrate was colonized by crinoids and corals, but no site was not studied in any more detail. Crutchley et al. (2009) show indication of chemoautotrophic fauna was found (Fig. 7). that all three seep areas of the Weka site (Weka A to C) are underlain with gas-rich sediments, with the southernmost and shallowest site, 4. Discussion Weka-A, at a BSR pinch-out. Comparing the depth at which these seeps occur (Table 1) with the 3.6. Ritchie Ridge gas hydrate phase boundary of pure methane hydrate, it is evident that all seeps are inside or just at the edge of the gas hydrate phase The first site from the Ritchie Ridge area, LM-1, was described by boundary (i.e. Faure B at Rock Garden). Seismic images show that all Lewis and Marshall (1996) as the site of Calyptogena shells “weakly seeps that were crossed by seismic lines have developed in connection bound with a muddy carbonate cement”. Thus, they named this site with deep reaching fractures, which provide migrations pathways Calyptogena Bank. Attempts to find indications of seepage from the through the hydrate stability field (Netzeband et al., this issue; reported position (given by fishermen) failed during TAN0616, no Crutchley et al., 2009-this issue). This is in contrast to observations by flare could be detected and no signs of morphological or backscatter Naudts et al. (2006) for the slope area west of Crimea in the Black Sea anomalies were found. However, a site 15.5 km to the south, named and for seeps observed more recently offshore Svalbard (Westbrook Builder's Pencil, was studied during TAN0616. Builder's Pencil et al., 2009). In both of these regions gas release only occurs above the (Fig. 12) was named for the shape of the flare observed during earlier gas hydrate phase boundary. However, the finding at the Hikurangi NIWA fisheries studies. Margin is in agreement with other seep sites such as Hydrate Ridge During TAN0616 the actual seep position was pinpointing during offshore Oregon (Suess et al., 1999). There are three sites described in flare-imaging surveys (Fig. 4) and subsequent DTIS transects across the Lewis and Marshall (1996) in the Cook Strait which are outside the gas site (Fig. 12). These seabed observations showed an extensive field of hydrate stability zone (LM-4, 5 and 11; Table 1). An influence of dead Calyptogena sp. shells together with live tube worms and meteoric water, as described by Orpin (1997) for carbonate chimneys occasional Bathymodiolus sp. mussels (Fig. 7). These assemblages are from the Otago Peninsula cannot be ruled out for these three, much described in more detail by Baco et al. (this issue). Compared to all other shallower seeps. seep sites, Builder's Pencil is the largest in area and much of the seafloor Despite the large number of seeps and the many hours of visual is almost completely shell-covered ( ∼400 by 600 m). The presence of observations, only rather small (max. few square meters) and isolated live chemoautotrophic organisms as well as the occurrence of a flare patches of the seafloor appeared to be active enough to support live proves that the seepage is still active whilst the vast quantity of dead populations of tube worms or clams within the different seep sites. clam shells across the site indicates that seepage must have been much Because the large chemoautotrophic clams and worms characteristic

18 J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx of seep sites are entirely dependent on the ﬂux of ﬂuids transporting seeps along the Hikurangi Margin. New cruises are planned beginning

H2S and/or CH4, their existence is a direct indication of the past and 2010 and these will further examine the biological communities of present activity of the seep. Only the seep sites at Bear's Paw, North seep sites and elucidate the history of methane seepage offshore New Tower, and Tui supported locally abundant populations of live Zealand's North Island. chemoautotrophic organisms, suggesting that these have been the most active seepage sites in recent history. Although live tube worms Acknowledgement were present at other sites, they were not abundant and at most sites only dead clam shells are seen. Together with the presence of massive The authors thank all participants, crew and scientists, who put so carbonate structures, these accumulations of dead shells are evidence much work and effort into the cruises described here. Thanks also go of active seepage over long periods in the past but which has now to the funding agencies that made these three cruises possible: New ceased. The opposite is true for the Faure Site, here substantial bubble Zealand Foundation of Research, Science, and Technology (C05X0302 fl release and thus uid advection has been observed, but the area to GNS Science), Capability funds of GNS Science and the National fl shows no indication of ourishing chemosynthetic life. Institute for Water and Atmospheric Research as well as the Naval fl This disparity, and the limited amount of active uid venting at the Research Laboratory (US) supported TAN0607. The National Institute seabed, highlights the question of the age of the seep sites and their for Water and Atmospheric Research (Capability Fund project transient behaviour. At Takahe on Opouawe Bank, no carbonates were CRFH073) and NOAA (NA17RJ1231 and NA050AR417076) supported fl found at the sea oor and no clams or tubeworms, only bacterial mats TAN0616. The Federal Ministry of Education and Research, Germany and beds of ampharetid polychaetes were seen. This, together with the (grants 03G0600D and 03G0191A) provided R/V SONNE and recovery of gas hydrates from 2.4 m sediment depth might indicate a additional grants for seismic and geochemical work. GNS Science ‘ ’ fl new seep that only established recently at the sea oor surface and thus (C05X0302) and NIWA's Capability Fund (CRFH073) supported the is too young for carbonates and an extensive chemoautotrophic fauna to SO191 cruise and related work in New Zealand. have formed. A similar change in activity is seen at Bear's Paw on We also thank Bryan Davy from GNS Science as well as Scott Omakere Ridge, here the amount of living tube worms and uncovered Nodder and Cliff Law from NIWA for additions to the manuscript. carbonates decreases from east to west indicating that the centres of Lindsay Gee, Maurice Doucet and Erin Heffron from IVS-3D are seep activity have migrated over time. thanked for the beta version of FMGeocoder and Doug Bergersen from At Opouawe Bank, there is also the appearance of a lateral migration Acoustic Imaging for an introduction in FMGeocoder and latest news of seep activity but in this case the age and maturity decreases from the about Fledermaus. We further would like to thank Christine Utecht, centre, the North Tower seep, towards the west and east. Piwakawaka in Martina Ikert, and Bettina Domeyer for their professional and fi the west shows de nite signs of active seepage but to lesser extend in indispensable logistic help behind the scenes of cruise SO191. JG space and activity than North Tower. Here a living fauna of clams, tube wants to thank Edna Huetten, who helped, as always, with the worms, bacterial mats and beds of ampharetid polychaetes together intricacies of the English language throughout the several versions of fl with a persistent are all indicate active seepage. In situ measurements this paper. of the total oxygen uptake and seabed methane emission rates obtained at North Tower revealed the highest values at the ampharetid polychaete beds in comparison to other cold seeps at the Hikurangi Appendix A. Supplementary data Margin and different geographical regions (Sommer et al., this issue). It is speculated that the ampharetid polychaete beds represent an early Supplementary data associated with this article can be found, in stage of metazoan colonization at seeps, creating a pathway for high the online version, at doi:10.1016/j.margeo.2010.01.017. microbial methane turnover and associated carbonate precipitation, which expedites the transition from soft sediment to a hard substrate References seep fauna (Sommer et al., this issue). Takahe, east of North Tower, shows no signs of chemoherm-type carbonates and thus is most likely Artemov, Y.G., Egorov, V.N., Polikarpov, G.G., Gulin, S.B., 2007. Methane emission to the hydro — an atmosphere by gas bubble streams in the Dnieper Paleo-Delta, the Black much younger. However, the occurrence of ampharetid beds and gas Sea. Marine Ecological Journal 1, 5–26. hydrate indicate intense methane seepage and in this respect indicates a Baco, A.R., Rowden, A.A., Levin, L.A., Smith, C.R., and Bowden, D.A. Initial characteriza- shifting of seep activity eastward from North Tower and in prolongation tion of cold seep faunal communities on the New Zealand Hikurangi Margin. Marine Geology, this issue. maybe even towards Papango. Baldwin, R.P., Lewis, K.B., 1991. Cook bathymetry. 2nd ed. New Zealand Oceanographic Institute Chart oceanic series 1:1,000,000. 5. Conclusions Barnes, P.M., Lewis, K.B., 1991. Sheet slides and rotational failures on a convergent margin: the Kidneppers Slide, New Zealand. Sedimentology 38, 205–221. Barnes, P.M., Mercier de Lepinay, B., 1997. Rates and mechanics of rapid frontal With 32 methane-related seep sites (Table 1), most of them accretion along the very obliquely convergent southern Hikurangi margin. New visually confirmed and physically sampled, the Hikurangi Margin is an Zealand Journal of Geophysical Research 102, 24931–24952. fl Barnes, P.M., Mercier de Lepinay, B., Collot, J.-Y., Delteil, J., Audru, J.-C., 1998. Strain area well suited to a multidisciplinary study of uid seepage at a partitioning in the transition area between oblique subduction and continental convergent margin, across a range of water depths, different tectonic collision, Hikurangi margin, New Zealand. Tectonics 17, 534–557. settings and different faunal habitats. Barnes, P.M.; Mercier de Lépinay, B.; Collot, J-Y.; Delteil, J.; Audru, J-C., and GeodyNZ team., 1999. South Hikurangi GeodyNZ swath maps: depths, texture and geological Opouawe Bank is the area with the highest frequency of occurrence interpretation. 1:500, 000. NIWA Chart, Miscellaneous Series 75. National Institute of seeps identified so far, having nine seeps visually observed and of Water and Atmospheric Research, Wellington. sampled, and four additional sites showing morphological and Barnes, P.M., Lamarche, G., Bialas, J., Henrys, S., Pecher, I., Netzeband, G.L., Greinert, J., backscatter expressions typical of seeps. Its close proximity to land at Mountjoy, J.J., Pedley, K., and Crutchley, G., 2009. Tectonic and geological framework for gas hydrate and cold seeps on the Hikurangi subduction margin, the south-eastern end of Cook Strait, and to Wellington's National New Zealand. Marine Geology, this issue. Institute for Water and Atmospheric Research (NIWA), makes the Bialas, J., Greinert, J., Linke, P., Pfannkuche, O., 2007. FS Sonne Fahrtbericht/Cruise Opouawe Bank an ideal place for future repeated monitoring of seep Report SO 191 New Vents. IFM-GEOMAR, Leibniz-Institut für Meereswissenschaf- ten, Kiel, Germany. 190 pp. activity development, potentially through moored instruments or Bohrmann, G., Greinert, J., Suess, E., Torres, M., 1998. Authigenic carbonates from the cabled observatories in the future. Cascadia subduction zone and their relation to gas hydrate stability. Geology 26, The cruises up to now only give a general overview of the 647–650. Campbell, K.A., 2006. Hydrocarbon seep and hydrothermal vent paleoenvironments: processes at work on this margin. The 23 papers in this special issue past developments and future research directions. Palaeogeography, Palaeoclima- (Table 2) cover all studied areas and give a first impression of the tology, Palaeoecology 232, 362–407.

J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx 19

Campbell, K.A., Francis, D.A., Collins, M., Gregory, M.R., Nelson, C.S., Greinert, J., Aharon, Kvenvolden, K.A., Pettinga, R., 1989. Hydrocarbon gas seeps of the convergent P., 2008. Hyrdocarbon seep-carbonates of a Miocene forearc (East Coast Basin), Hikurangi margin, North Island, New Zealand. Marine Petroleum Geology 6, 2–8. North Island, New Zealand. Sedimentary Geology 204, 83–105. Law, C.S., Nodder, S.D., Mountjoy, J., Marriner, A., Orin, A., Pilditch, C.A., Franz, P., Campbell, K.A., Nelson, C.S., Alfaro, A.C., Boyd, S., Greinert, J., Nymann, S.L., Grosjean, E., Thompon, K. Geological, hydrodynamic and biogeochemical variability of a New Logan, G.A., Gregory, M.R., Cooke, S., Linke, P., Milloy, S., Wallis, I. Geological imprint Zealand deep-water methane cold seep during an integrated three-year time- of methane seepage on the seabed and biota of the convergent Hikurangi Margin, series study, Marine Geology, this issue. New Zealand: Survey of core and grab samples. Marine Geology, this issue. Lewis, K.B., 1980. Quaternary sedimentation on the Hikurangi oblique-subduction and Chiswell, S.M., 2002. Wairarapa Coastal Current influence on sea surface temperature in transform margin, New Zealand. In: Balance, P.F., Reading, H.G. (Eds.), Sedimen- Hawke Bay, New Zealand. New Zealand Journal of Marine and Freshwater Research 36, tation on oblique-slip mobile zones: Special publication of the International 267–279. Association of Sedimentologists, 4, pp. 171–189. Chiswell, S.M., 2003. Circulation within the Wairarapa Eddy, New Zealand. New Lewis, K.B., 1990. Seep faunas and limestone chimneys. Professional fisherman 4 (6), Zealand Journal of Marine and Freshwater Research 37, 691–704. 16–17. Collot, J.-Y., Delteil, J., Lewis, K.B., Davy, B., Lamarche, G., Audru, J.-C., Barnes, P.M., Lewis, K.B., Pettinga, J.R., 1993. The emerging, imbricate frontal wedge of the Hikurangi Chanier, F., Chaumillon, E., Lallemand, S., Mercier de Lepinay, B., Orpin, A.R., margin. In: Ballance, P.F. (Ed.), South Pacific sedimentary basins. Sedimentary Basins Pelletier, B., Sosson, M., Toussaint, B., Uruski, C., 1996. From oblique subduction to of the World 2, Basins of the Southwest Pacific. Elsevier, Amsterdam, pp. 225–250. intra-continental transpression: structures of the southern Kermadec-Hikurangi Lewis, K.B., Marshall, B.A., 1996. Seep faunas and other indictors of methane-rich margin from multibeam bathymetry, side-scan sonar and seismic reflection. dewatering on the New Zealand convergent margins. New Zealand Journal of Marine Geophysical Research 18, 357–381. Geology and Geophysics 39, 181–200. Collot, J.-Y., Lewis, K.B., Lamarche, G., Lallemand, S., 2001. The giant Ruatoria debris Lewis, K.B. Collot, J-Y., Davy, B.W., Delteil, J., Lallemand, S.E. Uruski, C. 1997. North avalanche on the northern Hikurangi margin, New Zealand; results of oblique Hikurangi GeodyNZ swath maps: depths, texture and geological interpretation. seamount subduction. Journal of Geophysical Research 106, 19271–19297. 1:500, 000. NIWA Miscellaneous Chart Series 72. National Institute of Water and von Cosal, R., Marshall, B.A., 2003. Two new species of large mussels (Bivalvia Atmospheric Research, Wellington. Mytilidae) from active submarine volcanoes and a cold seep off the eastern North Lewis, K.B., Collot, J.-Y., Lallemand, S.E., 1998. The dammed Hikurangi Trough: a Island of New Zealand, with description of a new genus. Nautilus 117, 31–46. channel-fed trench blocked by subducting seamounts and their wake avalanches Crutchley, G.J., Pecher, I.A., Gorman, A.R., Henrys, S.A., and Greinert, J., 2009. Seismic (New Zealand-France GeodyNZ Project). Basin Research 10, 441–468. imaging of gas conduits beneath seafloor seep sites in a shallow marine gas hydrate Lewis, K.B. Barnes P.M., Collot J-Y., Mercier De Lépinay B., Delteil J., and GeodyNZ Team. province, Hikurangi Margin, New Zealand. Marine Geology, this issue. 1999: Central Hikurangi GeodyNZ swath maps: depths, texture and geological Davey, F.J., Hampton, M., Childs, J., Fisher, M.A., Lewis, K.B., Pettinga, J.R., 1986a. Structure of interpretation. 1:500, 000 NIWA Chart, Miscellaneous Series 77. National Institute a growing accretionary prism, Hikurangi Margin, New Zealand. Geology 14, 663–666. of Water and Atmospheric Research, Wellington. Davey, F.J., Hampton, M., Childs, J., Fisher, M.A., Lewis, K.B., Pettinga, J.R., 1986b. Lewis, K.B., Pantin, H.M., 2002. Channel-axis, overbank and drift sediment waves in the Structure of a growing accretionary prism, Hikurangi margin, New Zealand. southern Hikurangi Trough, New Zealand. Marine Geology 192, 123–151. Geology 14, 663–666. Linke, P., Sommer, S., Rovelli, L., McGinnis, D.F. Physical limitations of dissolved Davy, B., 1992. The influence of subducting plate buoyancy on subduction of the methane fluxes: The role of bottom layer process. Marine Geology, this issue. Hikurangi-Chatham Plateau beneath the North Island, New Zealand, In: Watkins, J., Liebetrau, V., Eisenhauer, A., Linke, P. Deciphering the geochemical record of cold seep Zhigiang, F., McMillen, K. (Eds.), Advances in the geology and geophysics of the carbonates and cold water corals from the Hikurangi Margin, offshore New continental margin, 53 ed. AAPG, pp. 75–91. Zealand. Marine Geology, this issue. Egorov, V., Luth, U., Luth, C., Gulin, M.B., 1998. Gas seeps in the submarine Dnieper Martin, R.A., Nesbitt, E.A., Campbell, K.A. The effects of anaerobic methane oxidation on Canyon, Black Sea: acoustic, video and trawl data. In: Luth, U., Luth, C., Thiel, H. benthic foraminiferal assemblages and stable isotopes on the Hikurangi Margin of (Eds.), MEGASEEPS Gas Explorations in the Black Sea, Project Report. Zentrum für eastern New Zealand. Marine Geology, this issue. Meres- und Klimaforschung der Universität Hamburg, Hamburg, pp. 11–21. Merewether, R.M., Olsson, S., Lonsdale, P., 1985. Acoustically detected hydrocarbon Ellis, S., Pecher, I., Kukowski, N., Xu, W., Henrys, S., and Greinert, J. Testing proposed plumes rising from 2-km depths in Guaymas Basin, Gulf of California. Journal of mechanisms for seafloor weakening at the top of gas hydrate stability, Rock Garden, Geophysical Research 90 3.075-073.085. New Zealand. Marine Geology, this issue. Naudts, L., Greinert, J., Artemov, Y., Staelens, P., Poort, J., Van Rensbergen, P., De Batist, Faure, K., Greinert, J., Pecher, I.A., Graham, I.J., Massoth, G.J., Ronde, C.E.J.D., Wright, I.C., M., 2006. Geological and morphological setting of 2778 methane seeps in the Dnepr Baker, E.T., Olson, E.J., 2006. Methane seepage and its relation to slumping and gas paleo-delta, northwestern Black Sea. Marine Geology 227, 177–199. hydrate at the Hikurangi Margin, New Zealand. New Zealand Journal of Geology Naudts, L., Greinert, J., Poort, J., Belza, J., Vangampelaere, E., Boone, D., Linke, P., Henriet, and Geophysics 49, 503–516. J.-P., and De Batist, M. Active venting sites on the gas-hydrate-bearing Hikurangi Faure, K., Greinert, J., Schneider v.D., J., McGinnis, D.F., Kipfer, R., Linke, P. Free and Margin, Off New Zealand: Diffusive- versus bubble-released methane. Marine dissolved methane in the water column and the sea surface: Geochemical and Geology, this issue. hydroacoustic evidence of bubble transport. Marine Geology, this issue. Nelson, C.S., Healy, T.R., 1984. Pockmark-like features on the Poverty Bay sea bed — Greinert, J., Bohrmann, G., Suess, E., 2001. Methane-venting and gas hydrate-related possible evidence for submarine mud volcanism. New Zealand Journal of Geology carbonates at the Hydrate Ridge: their classification, distribution and origin. In: and Geophysics 27, 225–230. Paull, C.K., Dillon, W.P. (Eds.), Natural Gas Hydrates: Occurrence, Distribution, and Netzeband G.L., Krabbenhöft, A., Zillmer, M., Petersen, C.J., Papenberg, C., and Bialas, J. Detection: Geophysical Monograph, 124, pp. 99–113. The structures beneath submarine methane seeps: Seismic evidence from Greinert, J., Artemov, Y., Egorov, V., De Batist, M., McGinnis, D., 2006. 1300-m-high Opouawe Bank, Hikurangi Margin, New Zealand. Marine Geology, this issue. rising bubbles from mud volcanoes at 2080m in the Black Sea: Hydroacoustic Nyman, S.L., Nelson, C.S., Campbell, K.A., this issue. Miocene tubular concretions in East characteristics and temporal variability. Earth and Planetary Science Letters 244, Coast Basin, New Zealand: Analogue for the subsurface plumbing of cold seeps, 1–15. Marine Geology, this issue. Henrys, S.A., Ellis, S., Uruski, C., 2003. Conductive heat flow variations from bottom Nikolovska, A., Sahling, H., Bohrmann, G., 2008. Hydroacoustic methodology for simulating reflectors on the Hikurangi margin, New Zealand. Geophysical Research detection, localization, and quantification of gas bubbles rising from the seafloor at Letters 30. doi:10.1029/2002GL015772. gas seeps from the eastern Black Sea. Geochemistry Geophysics Geosystems 9, Henrys, S.A., Reyners, M., Pecher, I.A., Bannister, S., Nishimura, Y., Maslen, G., 2006. Q10010. doi:10.1029/2008GC002118. Kinking of the subducting slab by escalator normal faulting beneath the North Orange, D.L., Breen, N.A., 1992. The effects of fluid escape on accretionary wedges: 2. Island of New Zealand. Geology 34, 777–780. Seepage force, slope failure, headless submarine canyons, and vents. Journal of Hornafius, J.S., Quigley, D., Luyendyk, B.P., 1999. The world's most spectacular marine Geophysical Research 97, 9277–9295. hydrocarbon seeps (Coal Oil Point, Santa Barbara Channel, California): quantifica- Orpin, A.R., 1997. Dolomite chimneys as possible evidence of coastal fluid expulsion, tion of emissions. Journal of Geophysical Research – Oceans 104, 20703–20711. uppermost Otago continental slope, southern New Zealand. Marine Geology 138, 51–67. Hütten, E., Greinert, J., 2008. Software controlled guidance, recording and post- Ostrovsky, I., McGinnis, D.F., Lapidus, L., Eckert, W., 2008. Quantifying gas ebullition processing of seafloor observations by ROV and other towed devices: the software with echosounder: the role of methane transport by bubbles in a medium-sized package OFOP. Geophysical Research Abstracts Vol. 10 EGU2008-A-03088. lake. Limnology and Oceanography – Methods 6, 105–118. Jones, A.T., Greinert, J., Bowden, D., Klaucke, I., Petersen, J., Netzeband, G., Weinrebe, W. Pecher, I.A., Henrys, S.A., 2003. Potential gas reserves in gas hydrate sweet spots on the Acoustic and visual characterisation of methane-rich seabed seeps at Omakere Hikurangi Margin, New Zealand. 2003/23 Institute of Geological and Nuclear Ridge on the Hikurangi Margin, New Zealand. Marine Geology, this issue. Sciences, Lower Hutt. Judd, A., Hovland, M., 2007. Seabed fluid flow: the impact on geology. Biology and the Pecher, I.A., Henrys, S.A., Zhu, H., 2004. Seismic images of gas conduits beneath vents Marine Environment, Cambridge University Press, Cambridge. 475 pp. and gas hydrates on Ritchie Ridge, Hikurangi Margin, New Zealand. New Zealand Katz, H.R., 1981. Probable gas hydrate in continental slope east of the North Island, New Journal of Geology and Geophysics 47, 275–279. Zealand. Journal of Petroleum Geology 3, 315–324. Pecher, I.A., Henrys, S.A., Ellis, S., Chiswell, S.M., Kukowski, N., 2005. Erosion of the Klaucke, I., Weinrebe, W., Petersen, C.J., Bowden, D. Temporal variability of gas seeps seafloor at the top of the gas hydrate stability zone on the Hikurangi Margin. New offshore New Zealand: Multi-frequency geoacoustic imaging of the Wairarapa area, Zealand Geophysical Research Letters 32. doi:10.1029/2005GL024687. Hikurangi margin. Marine Geology, this issue. Pecher, I., Coffin, R., Henrys, S., 2007. Tangaroa TAN0607 Cruise Report: gas hydrate Krabbenhöft, A., Netzeband, G.L., Bialas, J., and Papenberg, C. Methane concentrations exploration on the East Coast, North Island, New Zealand. GNS Science Report from ocean bottom stations and their relation to seismic structures. Marine 2007/29. 119p. Geology, this issue. Pecher, I.A., Henrys, S.A., Wood, W.T., Kukowski, N., Crutchley, G.J., Fohrmann, M., Kukowski, N., Greinert, J., and Henrys, S. Morphometric and critical taper analysis of the Kilner, J., Senger, K., Gorman, A.R., Coffin, R.B., Greinert, J., and Faure, K. Focussed Rock Garden region, Hikurangi Margin, New Zealand: implications for slope stability Fluid Flow on the Hikurangi Margin, New Zealand – Evidence from Possible Local and potential tsunami generation. Marine Geology, this issue. Upwarping of the Base of Gas Hydrate Stability. Marine Geology, this issue.

20 J. Greinert et al. / Marine Geology xxx (2010) xxx–xxx

Ridd, M.F., 1970. Mud volcanoes in New Zealand. American Association of Petroleum enhanced dewatering, benthic material turnover and large methane plumes at the Geology Bulletin 54, 601–616. Cascadia convergent margin. Earth and Planetary Science Letters 170, 1–15. Sauter, E.J., Muyakshin, S.I., Charlou, J.-L., Schlüter, S., Boetius, A., Jerosch, K., Damm, E., Suess, E., 2010. Marine cold seeps. In: Timmis, Kenneth N. (Ed.), Handbook of Foucher, J.-P., Klages, M., 2006. Methane discharge from a deep-sea submarine mud Hydrocarbon and Lipid Microbiology, Vol. 1; Part 3: Transfer from the Geosphere to volcano into the upper water column by gas hydrate-coated methane bubbles. the Biosphere. Springer, Heidelberg, pp. 187–203. Earth and Planetary Science Letters 243, 354–365. Thurber, A.R., Kröger, K., Neira, C., Wiklund, H., Levin, L.A. Stable isotope signatures and Schneider v.D., J., Brockhoff, J., Greinert, J., 2007. Flare imaging with multibeam methane use by New Zealand cold seep benthos. Marine Geology, this issue. systems: Data processing for bubble detection at seeps. Geochemistry Geophysics Townend, J., 1997. Subducting a sponge: minimum estimates of the fluid budget of the Geosystems 8. doi:10.1029/2007GC001577. Hikurangi margin accretionary prism. Geological Society of New Zealand Schwalenberg, K., Wood, W., Pecher, I., Hamden, L., Henrys, S., Jegen, M., and Coffin, R.B. Newsletter 112, 14–16. Preliminary interpretation of CSEM, heatflow, seismic, and geochemical data for Walcott, R.I., 1978. Present tectonics and late Cenozoic evolution of New Zealand. gas hydrate distribution across the Porangahau Ridge, New Zealand. (a) Marine Geophysical Journal of the Royal Astronomical Society 52, 137–164. Geology, this issue. Westbrook, G.K., Thatcher, K.E., Rohling, E.J., Piotrowski, A.M., Pälike, H., Osborne, A.H., Schwalenberg, K., Haeckel, M., Poort, J., and Jegen, M. Evaluation of gas hydrate deposits in Nisbet, E.G., Minshull, T.A., Lanoiselle, M., James, R.H., Hühnerbach, V., Green, D., an active seep area using marine controlled source electromagnetics: Results from Fisher, R.E., Crocker, A.J., Chabert, A., Bolton, C., Beszczynska-Möller, A., Berndt, C., Opouawe Bank, Hikurangi Margin, New Zealand. (b) Marine Geology, this issue. Aquilina, A., 2009. Escape of methane gas from the seabed along the West Sloan, E.D., 1998. Clathrate hydrates of natural gases. CRC Press, Boca Raton, Fla. 641 pp. Spitsbergen continental margin. Geophysical Research Letters 36, L15608. Sommer, S., Linke, P., Pfannkuche, O., Treude, T., Niemann, H. Carbon flow through a novel doi:10.1029/2009GL039191. seep habitat dominated by dense beds of ampheretid polychaetes. Marine Geology, Wood, R., Davy, B., 1994. The Hikurangi Plateau. Marine Geology 118, 153–173. this issue. Suess, E., Torres, M.E., Bohrmann, G., Collier, R.W., Greinert, J., Linke, P., Rehder, G., Trehu, A., Wallmann, K., Winckler, G., Zuleger, E., 1999. Gas hydrate destabilization: